MBB are the only real consulting firms

The best role is reserved for best the rest get a lot back office work and boring research and deck making

No. There are a bunch of consulting firms that operate in niche domains, but do top notch management consulting work. Accenture, OW, A&M, Dalberg and the likes.

Deloitte and Accenture are huge in global scale but are not MBB. It's just a useless tag.