There's a good reason why I saved Buggy until last.

Buggy is the first devil fruit user faced by Luffy, but became the butt of jokes after being defeated but kept alive for the majority of the series where he seems to indirectly influence major events following the breakout of Impel Down, effectively his position of power was achieved not through power but by clout as he knows Shanks personally and is at least acquainted with a number of major players, this allowed him to ascend to the Emperor's position with his Cross Guild group where he places bounties on marines, the fact that Crocodile and Mihawk join him for this, really helps, although both former Warlords wouldn't hesitate to use him as the scapegoat if things go wrong, this also calls the bounty system into play as it's less power level measuring and more level of clout and overall danger level in the world.
Also worth noting is that Buggy is one of the hardest pirates to kill with him able to split into pieces, it would become seriously OP if awakened.
Buggy essentially achieved his position through clout alone despite being a mid boss at best, some seem to think he would even grab the One Piece only to lose it to Luffy as part of the ending.