
Is Kyoraku’s Bankai useless, or even counterproductive, against enemies with regeneration?
What I mean is that the first act can be abused very easily by enemies with regeneration: they can hurt Kyoraku without worrying about the consequences, while the illness might not affect them at all or its effects could be heavily mitigated.
Likewise, the throat-cutting in the final act would be completely useless. The only useful part of the Bankai would be the sea, and even that could fail if the enemy has as much or more reiatsu than Kyoraku.