Since we learned that the shinigami badge was weakening Ichigo, I wondered how the fight could have gone differently.
- Full strength, In Character
- Grimmjow can not use his resurrection
- No hollow interruption
- Battle takes place in Karakura Town
There are 3 reasons why I believe Ichigo got weaker after the SS arc -
1. The badge suppressed his rieatsu.
2. He lost his resolve after the fights with Byakuya and Yammy.
3. Juhabach suppressed his shinigami powers to make him more hollow-like
That said, I believe Ichigo takes it casually. Coz in the HM arc, Kenpachi and Byakuya were implied to be rivals (aka equals like Shunsui and Ukitake), and this version of Ichigo did beat Byakuya