I think people have misunderstod what the yonko and the seven warlords of the sea system is.I think that the main reason for why the yonko are said to be stronger then the seven warlords of the sea is because of their influence upon the world.It's not about strength i think the yonko system was put in place for people that the citizens of the one piece world would genuinly wanna follow.

I think the main reason for why the seven warlords aren't admired as much is because they have no intrest in it beyond getting their own needs met.

Boa hancock hates men.Doflamingo is a psychopath.Gecko Moria just uses people while doing no work.While crocodile just wants to destroy everything.Mihawk has no intrest in forging any sort of alliance because it wouldn't improve his combat strength.While Edward weevil just wants to destroy the world because he has daddy issues.Then there's buggy i honestly just think he was bumped up into his current yonko position because the gorosei didn't do their homework on him.I think luffys new bounty just clarifies that you can be a pirate with a three billon dollar bounty without having to follow anyone