Buggy wouldve been an admiral at this point if he was a marine because he is a gag character that always seems to get to higher places based on pure luck and accident, you really dont understand his character do you? He(Oda) would find a way.
Admirals are the strongest they are tested if theya re strong enought to be an admiral .
There is 2 admirals candidate that did"nt cuted it .
Buggy not gettin to admiral tittle without a massive strenght upgrate.
The living proof of that is aramaki and fujitora both were not part of the navy and got recruited and put admiral direclty because of their strenght .
Admiral is a strenght position .