If he was that exceptional he'd have exceeded his ranks bounty like garp has.
My point is exactly that: he might be stronger than Sengoku, but Sengoku too was that strong. He was someone put by Roger and WB on par with Garp.
FA are simply 5B individual
* Anyway, Garp, in fact, had the bounty he deserved. He refused to be an Admiral, but he was offered the promotion multiple times.