It annoys me to no end that people keep bringing up that Gojo let his guard down at the end of the fight like it's some kind of confirmation that he's stronger and Sukuna only won because of plot. Gojo's big turnaround moment in the where he gains control of the fight *entirely* relies on Sukuna getting cocky and assuming Gojo doesn't have any tricks up his sleeve. They made the same mistake. Sukuna almost lost the fight because of his blunder, Gojo did.

What happens in a scenario where both characters are emotionless robots who are 100% locked in at all times? Gojo would avoid the WCS like Gege said. But I doubt he would ever be in such a good condition as he was in canon. In this scenario Sukuna would sense the red coming and either dodge or defend with DA and just get some burns again. This means Gojo doesn't land that crazy offguard red + black flash combo. 

It really cannot be understated how much damage this hit did. It fucked Sukuna up to the point where he was forced to hide in the shadows to recover and rely on Mahoraga to do most of the actual fighting. Even two chapters later Sukuna was still healing, even though Gojo did not land a single hit on Sukuna in the meantime. And that's ignoring the black flashes, even if we assume he still lands the black flashes after this one. It still means he gets his output and RCT back much later. 

The fight would go pretty similar to canon, with Sukuna summoning Mahoraga and Agito to put more pressure on Gojo and speed up adaptation, but this time Sukuna would be a lot healthier (meaning he can participate a lot more actively) and Gojo wouldn't get his initial black flash amp until halfway through chapter 234.  This means Mahoraga gets more time to adapt, and Sukuna gets more time to copy the WCS. The timing was already *very* close. If Gojo has to start his Unlimited Purple plan just a little later Sukuna will have figured out the WCS and be able to spam them by just making his domain sign.

"Gojo only lost because he let his guard down." That's true, and if Sukuna didn't let his guard down here Gojo would not even get that far.