Bounties are a fickle because roles matter. Likes of Kaido and BM won't break it past 3 billion either if they didn't have strong crews. Bounty is never about just individual prowess unless you're a sole man with no crew behind you.
So, how are we judging Akainu/Kizaru/etc? Based on their strength completely? Then I don't think we have anyone to compare with to negate inflation lol
Maybe when Mihawk gets his bounty, we'll have better answer.