Only reason I can think of for luffy being an emperor and not kidd and law is influence. Luffy got Grand fleet and is Wano will probably tie up with strawhats not law or kidd.
they have their own territory.
same goes for buggy. literally he made impel down prisoners his followers.
shanks has ties with gaints and elbaf.
blackbeard has level 6 impel down character as his surbordinate and 2 op fruit which gave him 2.247 bounty.