I always interpreted it as Kenny suppressing himself lead to him nearly dying which led to him getting boosts which put him closer to his original strength. Nearly died against Ichigo and showed up Nnoitra level. Nearly died against Nnoitra and showed up Yammy level. Even post Muken where he doesn’t deal with his subconscious suppression anymore, nearly died against Gremmy and the Femritters, healed up, severely injured by Pernida, healed up again, shows up God Size Gerard level. Severely injured in the Gerard fight, returns stronger than Hikone and Ikomi
Ichigo basic strength outside of hollow form went up as well. At <50% was able to cancel out Res Yammy’s Cero Oscuras at while his previous Masked Bankai amped Getsuga’s couldn’t damage Res Ulq. Res Yammy’s physical strength is > R2 Ulq’s entire arsenal, let alone an order of magnitude amped Cero from Yammy. He also damaged Gin who scales above the Espada, with a Getsuga. And throughout the story in general, while Ichigo is a weird case with his Zan spirits influencing his power different from anyone else, it’s still a fact that Urahara stated the fastest way to grow was through life and death experiences and proved it with Ichigo, so it’s not a stretch to say Ichigo’s growth continued like this
Toshiro went from nearly being put on a T Shirt at 20% by Fraccion Shaolong to outscaling Res Espada 6 Luppi’s 8x amped attack with a bit of charge time, then scales to Res Halibel though tbf I don’t remember if it was said he trained during the Arrancar/FKT arcs if we count them as 1 story wise, rather than between arcs like we know he does