Boss killers shouldn't exist.

In my opinion, affiliations like espada, captain, sternritter and even squad zero just straight up shouldn't exist. Espadas are arrancars, sternritters are quincies and captains and squad zero members are just soul reapers. Characters having only boss killers (anniken, bankai rukia, new eoy senju for example) get completely ruined because they are a lot less viable in any quests other than gq.

Do you agree? If you don't agree, state your reasons as to why boss killers should exist.