You're still saying the same thing.. there's no frs without the rasengan either, but that does not mean the rasengan itself cannot be enlarged.. so again that example does not favour your argument at all.
I don't know why you're bringing up Rasenshuriken. Hashirama isn't adding new elements to his Mokuton when he upgrades the Wood Dragon to the Wood Human. From Wood Dragon to Wood Human to Shinsuusenju, the only difference is more chakra, just like Naruto's normal Rasengan variants. That's where the comparison comes from. If Hashirama concentrates his full power on a Wood Human it will become Shinsuusenju. If Naruto concentrates his full power on a Rasengan, it will become a different jutsu entirely, Chou Odama Rasengan.
The mere fact that full kurama doesn't make gamabunta look like a rat which you yourself have pointed out he does in comparison to PS, should suffice as proof that kurama is nowhere near edo madara's PS in size..
Gamabunta is as big as Kurama's head with ears included. I'll just scale it directly so this isn't a constant talking point.
Like are we to also assume spiral zetsu's shinsusenju is the same size as hashirama's because "fixed size"?
Not to mention your arguments contradict each other as both hashirama and madara used wood dragon on full and 50% kurama respectively so if the wood dragon also has a fixed size as you say, it shouldn't have been comparable to both those kuramas.
Though that argument itself is silly as we do know wood dragon can be made to vary in size ranging from biju size, to smaller ones more comparable to human size:
So your whole fixed size notion is non existent
Nothing implies that Zetsu's Buddha is even the same jutsu as Hashirama's. It's his own personal construct and has a different design to Hashirama's Buddha. You're talking as if every scan is 100% consistent, I am not. Also the Wood Dragon used on Kurama & Madara are clearly different Wood Dragons.
The Wood Dragon on the Mokujin during the War arc is comparable to Madara's V3 Susano'o, which makes it Biju sized the same as it was when used by Edo Madara. Yet you're claiming that the Mokujin used there is the biggest one for some reason. The Wood Dragon has a lot of length. It's long enough to wrap around both 50% & 100% Kurama.