Kubo said in an omake SS actually grew stronger after Aizen's defeat. For example, Hitsugaya has fully mastered his bankai, and Renji's bankai changed a little. Not that it matters now, since bankai is useless against Vandenreich. And of course, these new enemies are nothing like we've seen before. They can even give Arrancars Quincy powers, dammit.
英雄メンバー / Eiyuu Menbaa / Hero Member
Post Thanks / Like
Re: Did Soul Society grow weaker?
Did Soul Society grew weaker? It depends what your understanding of the word "weaker" is & how you choose to apply it.
To Yhwach, the softening up of Soul Society's mentality made them weaker. In other words, the mindset of SS, specifically the divisions enabled the weakening.
If SS never slept during the time of peace (as Yhwach puts it), then it's is likely that they would continually contrive new systems, new techs, new equipment to further improve the security of their homes & individuals that live there. The old ruthless SS would pursue their goals through any means they deem necessary, weather it be killing their own kind to achieve a purpose or using humans however they pleased & etc
The medallion which steals Bankai, the improvement of Letzt Stil to Vollstandig are just a few powerful examples to connote that SS enemy, the Quincy weren't sleeping.
However, had SS pursue that way of doing things then they would be nothing more than thugs, animals, malevolent beings.