You're going this and that way when the matter is a million times easier to explain.
We have two guys supposedly in their prime squaring up against the same old fuck.
For Kizaru it went like this:
For Blackbeard it went like this:
So don't tell me some crap about Aramaki not being on BB's level. In comparison Teach looked like the OP world's biggest bitch.
If BB negged a warlord, Ryo already defeated a stronger warlord.
If Teach doesn't beat Law who is roughly on Old Ray level he got nothing on an Admiral let alone fucking Akainu.