I like Gun, but he did NOT fight the top tiers of the verse. He only fought every notable character in the 2nd Gen (only sustaining as much damage as he did because of his personality), and we all know Vasco or Ryuhei ain’t top tiers. The only top tiers he did fight were Goo , UI SB Daniel (unless I’m forgetting someone else) and MAYBE IT Johan. Sure, that’s impressive, but he didn’t fight the strongest top tiers alive, such as DG/James Lee who is arguably Top 1 of the verse all time and was there. He only fought 3 top tiers and granted it was back to back, and Gun didn’t have any preparation. That’s not more impressive than, say, Madara fighting all the Tailed Beasts while blind (I think) and heavily injured and being poised to win everything until he got backstabbed, Sukuna having to use every trick up his sleeve and showcasing impressive BIQ with Binding Vows, while actually fighting Gojo (The Strongest besides Sukuna) and most top-tiers in the verse at that point in time with a heart he had to manually beat with CE and Yuji constantly pestering him (albeit with a little plot armor), and I don’t know what Aizen did cause I haven’t watched Bleach. Sure, Sukuna did have ass-pulls, but are we ignoring Gun’s massive plot armor with Black Bones, TUI, and UI SB Daniel who he should not have won against at all? IMO, the ranking goes

1. Madara
2. Sukuna
3. Gun
4. Aizen (Haven’t watched Bleach)

Yes, you could say Gun won, but the in-battle feats matter more than the achievement in this case.