It did for a while, yeah, but it's really not that much of a surprise that a long running manga would improve its art over time. JoJo alone is a pretty big sign of that being a thing that happens, where you'd almost swear the series changed artists between its first chapter and now if you didn't see the comparison chart showing Araki's style improving and evolving over time.
The thing with Bleach is that, while that improvement did exist, it also eventually started getting worse as it drew closer to its end. That's the more surprising thing, at least when considering that the other mangas that have dipped in art quality had other circumstances (re: Togashi's health, Kishimoto's switch to digital drawing) that don't quite exist for Bleach.
