This alone should end the debate as of now.
"What surpasses the HORIZONS of sorcerors, cursed sprits, and strong fighters is overwhelming aggression that DISREGARDS ALL else... like a calamity."
Especially in context that the person being addressed, has the potential to be on or above Gojo's level.
Gojo USED to be like a calamity, specifically in the Toji fight, when he was so in tune with his sense of self, like Sukuna and Mahito, which is expressed with him not even caring that Riko or Geto was dead, he was just overcome with the absurdity of his own power, but as of now he currently isn't that way anymore. Maybe when he comes out of the box and finds out Nanami died, Nobara (possibly) died, Yaga died, etc. he will revert, but as of now he is essentially gatekept.
Add on top of that, that Kenjaku has now verbatim stated he is the strongest sorcerer he has ever known, albeit from 400 years ago, though this includes the Six Eyes and Limitless user running around.
Allow me to direct you to this excerpt from the fanbook.
"during the Heian period when jujutsu sorcery was at its PEAK"
"the birth of Gojo Satoru, the current head of the clan and the strongest jujutsu sorcerer in modern times"
I think the word choice here is very distinct and intentional. Given that the Heian era is the peak of jujutsu, and the true difference of that being exemplified that people from only 400 years ago, not even 1000, are pressing the current top tiers of the modern day to their absolute limits, got essentially soloed by Sukuna. Coupled with the fact that this excerpt specifies Gojo as the strongest in the modern era, after talking about the Golden age being the PEAK, I think there is an implication there.
Not only was Sukuna grossly strong back then, but as we learned in chapter 2, the fingers grow stronger EVERYDAY.
So given that its been 1000 years, when Sukuna comes back, he'll be even stronger than he was back then.
Now add on that based on feats and statements he has the
-Best Domain Expansion, being described as Godlike
-Best Reverse Cursed Technique, being able to revive himself and Yuji even from the DEAD
-Presumably the deepest knowledge and understanding of jujutsu and cursed energy
-A busted cursed technique
-Defeated a being that killed a six eyes + limitless user in the past, with relative ease at not even close to full power
And the narrative fact that when Gojo comes out of the box, if he is stronger than Sukuna, there are practically 0 stakes and genuine tension is almost nigh impossible to create given Sukuna's character.
Another noteworthy thing is that Kenjaku (probably the smartest character in the verse) had Sukuna as a contingency plan to deal with Gojo, if prison realm didnt work (and we all saw how effective THAT was). And his ONLY reservation was simply due to him not being sure if he'd work with them. Never a concern for if he was strong enough.
One last little tidbit is the knowledge gap. Gojo knows almost nothing about Sukuna, while Sukuna has seen purple, his domain, pretty much everything Gojo has to offer, and is disintersted, he only thing he seems to be invested in to any degree is Megumi's potential.
I'm sure there's some other arguments I've come up with that I'm forgetting, but this is sufficient for now.
@LANJI CUCKSMOKE Here you go the official Sukuna Manifesto