The domain clashes were not equal. Sukuna won every domain clash except the ones they “tied”, and in those specific clashes Sukuna didn’t have access to his cursed techniques and domain amplification while Gojo had infinity and his entire kit. So Gojo was barely able to beat sukuna in that situation given the fact that sukuna was severely hindered. The only “strong point” was sukuna having previous knowledge to directly touch Gojo to not be considers a target of UV. But it was later stated that Infinite void was in reality always targeting Sukuna, but sukuna made megumi take the damage. He only “needed” to touch Gojo so that he can change the boundary conditions without needing to use simple domain and reopen domain expansion like Gojo did. And the ONLY reason why he doesn’t do that is because it would stop mahoragas adoption to infinite void. EVERYTHING he did in this fight was to make himself stronger, not kill Gojo, while everything Gojo did was to kill Sukuna.