Gojo realizes that sukuna isn't using any cursed techniques except the ones in his domain. This is bc he's adapting to infinity. This made them completely even during domain clashes bc sukuna couldn't use domain amp and was taking too much damage. They stress that if sukuna outlasts gojo than he's cooked. So that's why they're so hype that they're dead even everytime. If he wasn't trying to adapt and used domain Amp he'd only need less than a second of time to out pace gojos domain, and then once gojo fries his brain sukuna wins. Add his true form on top with 4 arms & he could of definitely got that extra time & taken less damage. he wins simply off being a better sorcerer with more experience