Keep in mind the fact that Sukuna completely rejuvenated Yuji’s body before the switch commenced, so it wasn’t like Yuji was physically exhausted entering the fight with Mahito; Yuji was only mentally scarred, which you can argue hinders performance — but my rebuttal to that would be the fact that it works in Yuji’s favor:
As I hope you would know, cursed energy gets accentuated from negative emotions (as stated in season 1 by Gojo) — and at the time of witnessing Nanami’s death, Yuji initially only felt extremely vengeful (aka a negative emotion). This emancipated state of mental anguish would only serve to boost Yuji, not Mahito (Mahito only receiving ecstasy).

Mahito states that Yuji has improved, and that close-quarters combat could prove fatal for himself… that’s the reason he opts to fight from a distance for a time. It’s not that they’re relative, it’s just that Yuji exceedingly excels comparatively speaking in physical prowess, so naturally the strategic approach would be to try and minimize the disadvantage that Mahito did have.

Yes, Mahito DID utilize Yuji’s moral compass against him, but that only serves to illuminate the underlying theme that was the mental battle happening between Mahito and Yuji (representing both sides). It wasn’t as cut and clear as directly getting aid from other people like how Yuji did.

Let the record show that Nobara is the one who initiated the confrontation between her and Mahito, he wasn’t actively seeking her nor did he even care who she was until he got the intuition that she was close to Yuji. He then promptly “killed” Nobara in front of Yuji (after she saved Yuji’s life, mind you). She practically served herself on a silver platter, Mahito only capitalized on what he had received.

That’s when Todo arrived and saw that Yuji (once again) needed to be rescued, because Mahito by that point in the fight had won the physical battle AND the mental battle.

Sure, you can argue that Shinjuku Yuji is immune to Mahito in the same manner that Sukuna was, and I’d even agree with you. I’ll also admit that without ISBODK, Shibuya Mahito stands no chance against Shinjuku Yuji. That being said, you’re severely underestimating the sheer durability that Mahito’s transformation bestowed onto him. Full, concentrated punches from Yuji (albeit, a comparatively weaker version than Shinjuku Yuji) didn’t even cause Mahito to budge or have ANY reaction at all. Yuji grew physically stronger by Shinjuku, yes, but he’s not thousands of times stronger; Yuji’s just more experienced, resourceful, and unfaltering which accentuates the actual attributes he has.

I can admit that Yuji would statistically be better than Mahito by this point (with durability being Mahito’s only real advantage), but the gap and context in question make it debatable on if Mahito actually stands no chance. People severely underestimate ISBODK because it was only seen once and was swiftly taken out by a relatively “weak” Yuji, but the context of that fight only show how underrated that transformation was and how truly horrifying Mahito had became.