The issues involved for the clash is Infinite Crisis #5, Superman Vol. 2 #224, Action Comics #836, and Adventures of Superman #224

For context about who is fighting who, New Earth Superman is fighting “Golden Age” Superman Kal-L of Earth-2, the Superman seen from 1938 to about 1956. This Superman has on a few rare occasions fought on relative decent footing with “Silver Age” (Later on “Bronze Age from 1971-1985) Superman Kal-El of Earth-1 who was seen from about 1956 to 1985. Earth-1 Superman being the infamous incarnation who could sneeze away solar systems, fly at the speed of infinity, survive the big bang, and eat kryptonite. Golden Age Superman went to “Heaven,” a pocket dimension separate from reality, alongside Lois Lane, Superboy Prime, and Alexander Luthor to live in a sort of idyllic exile after the Infinite Crisis. I think it would be safe to assume, having aged over the years after the Crisis on Infinite Earths without constant conflict tempering him and the Sun empowering him that he is effectively past his prime and far weaker than his heights seen before the Crisis. However that didn’t stifle his power too greatly, as he was able to break the barrier of this dimension and reach the universe of New Earth in Infinite Crisis #1. However, reading the issue it is found that Superman is taking what he perceives as hours trying to punch out the barrier and his fist was getting crushed and injured doing this, so it was with a great amount of effort over time that he even succeeded in this feat.

It should be noted that Infinite Crisis is written to serve as a commentary on the difference in themes and plotlines in Pre-Crisis and Post-Crisis. New Earth Superman is supposed to represent the Post-Crisis themes of moral ambiguity, maturity, and the shades of gray between good and evil. Earth-2 Superman represents the perceived morally absolutist ideal of Superman and the non-gradient duality between black and white in Pre-Crisis. Superboy Prime represents those accustomed to Pre-Crisis who zealously defend its purported ideals. Earth-2 Superman started the Infinite Crisis hoping he could keep Lois Lane alive, however this fails and she still dies, causing him to blame her death on New Earth Superman. This initiates their clash.

The multiverse at the time was inherently unstable and is only capable of holding one Earth, that being the New Earth of Post Crisis. However, through Alexander Luthor’s machinations, Earth-Two is spawned which would inherently disrupt the already tenuous balance of the current paradigm, and the Multiverse was already very likely unstable and already breaking down as the fight would actually commence.

she official website page for Infinite Crisis #5 states the following:

“The DCU shakes apart as Superman of Earth 2 finally confronts our Superman. Meanwhile, heroes are disappearing throughout the DC Universe, a transformed villain returns, and the mystics of every world and dimension seek help from the very Spirit that is destroying them.”
~ DC Comics Storepage

However, I do not think this quote should be literal because for one thing, they used “DCU” instead of just “the universe.” DCU means the general shared storylines in DC, not the physical space-time continuum itself, ergo the fight is shaking the DCU as in it’s further causing mayhem and chaos plotwise. I will further explain why it is likely metaphorical.

The main crux of the argument is from Adventures of Superman #224, where it’s stated that the clash between New Earth and Earth-2 Superman have shattered the boundaries of space and time, which alongside the statement above gives the notion they physically shook the space-time continuum which is thus universal space-time manipulation. This is combined with the fact that they are stated on several occasions to have shattered/broken “The world” and that they seemingly are reliving entire timelines before shattering.

I could be wrong here, but for one thing it seems that everyone has assumed this was spoken by a narrator, which isn’t the case. If one looks at the emblems at the top corners and reads the issue, they will see it is both New Earth and Earth-2 Superman thinking this. Why is this important? Well neither were in the greatest mindset at the time of the fight; Golden Age Superman is angry, bloodlusted, and focused on killing New Earth Superman meanwhile New Earth Superman is mostly focused on just surviving and keeping up with Golden Age Superman. So they aren’t in a lucid enough mindset to really analyze or know the scope of their clash I would believe.

That leads me to the first quote:

“The struggle between us has shattered the boundaries of space and time.”
~ Both Supermen

So right off the bat, this wasn't stated by an unbiased omniscient narrator. Notice how these text bubbles have two different emblems of superman and a different color gradient. Black text = Post Crisis Superman and Red text = Golden Age Superman. That is because this is not a narrator describing the events, but the two Supermen thinking the same thing. These two were angry, confused, and in a mentally unwell state at the moment and wouldn't be sufficiently reliable narrators aware of their surroundings.

More importantly, this doesn’t literally refer to them destroying the universe. What it is, in fact, is the two Supermen concurrently believing the other to be responsible for the crisis at hand. New Earth Superman believes Golden Age Superman has risked the universe to destruction by attempting to revive Earth-2, while Golden Age Superman believes New Earth Superman is responsible for the crisis by not serving as an ideal role model and struggling at the face of forces like Doomsday, Parallax, and Imperiex, which Superman has always failed to cleanly prevent with a 100% happy ending or without sacrifices. They see each other as responsible for letting the universe to start dying, not that they actually directly threatened it through their power. In both of their eyes, the other Superman has brought the universe to its death throes due to their conflicting worldviews.

Now let’s go back to the main quote, the second one:

“The struggle between us has shattered the boundaries of space and time.”
~ Both Supermen

For one thing, shattering the boundaries of space and time alone doesn’t necessitate a quantifiable universal rating unless the actual range is universal which I shall disprove after this, but furthermore the context later reveals that they are referring to their ability to witness and experience their opponent’s lives, effectively bypassing their subjective reality and fall into another. They aren’t shattering the boundaries of space and time on a universal cataclysmic scale, they are shattering each others’ localized subjective reality’s boundaries which lets them relive each other's experiences rapidly and to their own liking. This was a wholly localized event and not universal in scope.

Let's entertain their punches did really break the boundaries of space and time, despite the fact that space and time was very unstable and delicate at the moment, this didn't mean on an actual destructive universal scale, and after these following paragraphs I shall debunk that assumption. Rather, this meant that, individually, Kal-El and Kal-L ' very essence and binding to space and time was being broken due to their conflicting world views. Notice how noone else comments on the universe shaking and shattering? Like Wonder Woman wasn't discussing it at all? Or anyone? It's because their worlds, their own subjective realities, their minds and memories were what was breaking, not the physical universe itself.

Dialogue only emphasizes that. Their own subjective memory and story of the universe were changing under their clash, most certainly due to the multiversal destabilization caused by Alexander Luthor which made such "feat," and this struggle (which is a reference as seen in-text to a struggle of ideals and identity. The themes of more cynical jaded Post Crisis vs the more idealistic naive Golden Age are struggling here) between Post Crisis Superman and Golden Age Superman couldn't be replicated under more normal circumstances because these were abnormal circumstances where a metaphysically and metatextually different Earth has spawned, destabilizing the multiverse. Noone else would feel the universe shaking because it wasn't the universe, like the physical space-time continuum, it was their universe, Kal-El and Kal-L's own spatio-temporal subjective realities and memories. They are experiencing this space-time manipulation in their minds, which can be seen how they are monologuing of these events as they fight.

It not being a universal scope event can be more clearly seen by the fact that:

#1. The actual fight between Kal-El and Kal-L in a physical sense only lead to citywide devastation

#2. In both Superman Vol. 2 #224 and Action Comics #836 we see Lois Lane and Jimmy Olsen respectively during the exact time of the fight living their life and not commenting on any actual collateral damage.

These first two also are odd in comparison to various other feats of a supposedly similar context across fiction:

*Take for comparison, the Goku vs Beerus clash, which was causing planets to get destroyed and was felt across the entire universe
*Or that the power struggle with Forsung shatters dead planets and creates suns in its wake
*Or that the battle with Infinity crumbles planets and makes galaxies fall, and threatens Earth from a great distance away

#3. Alexander Luthor doesn’t comment on any spatio-temporal shattering at all which would be a big deal given his project at hand. He would be one of the most important characters to comment on such a supposed feat if it happened, as it is in his best interests to be aware of any cosmic phenomena occuring when he is himself doing a cosmic scaled project. Yet he doesn't.

And thus, to sum it up:

*The feat was intended to be a metaphorical reflection of conflicting worldviews
*The narrators were the two Supermen, not an omniscient narrator, and they were in an enraged and unreliably unstable mindset
*Any reality shattering events were all in their head and on a mental level, not physical
*The feat left little to no collateral damage that suggested such a thing was happening, with the actual fight resulting with no more than the destruction of a city
*Noone, not even characters who should be invested in what is happening to the cosmos such as Alexander Luthor, ever commented on any spatio-temporal destabilization occuring or even felt any surge of energy or shockwaves. Nothing

So I don't agree with using this feat. It's not even an outlier. It's outright unusable and not a viable or real feat.