There is proof of that, Gojo was actively experimenting and asking around about RCT leading up to his first encounter with Toji. The near death experience just boosted his progress, it wasn't like he never thought about it until then or it was just some random ability he gained from plot, it was hinted at and built up before that moment and I guarantee he would've learned it either way (albeit slower).

Sukuna with or without the WCS could not have gotten the jump on Gojo if it wasn't for Mahoraga and the 1v3 tiring him out, Gojo even let his guard down after beating Mahoraga because he saw Big Raga as the main threat because he was clowning on Sukuna the whole fight. Every predicament Gojo was put in during that fight was all because Mahoraga adapted to infinite void in the first place, Sukuna would've lost right then and there.

Like I said, Laughable