With the admirals, it's an all or nothing when it comes to CoC. Either all admirals have it or none and we already know Sengoku and Garp have it. CoC is common according among those who have made a name for themselves according to Ray and Chinjao. A couple of high tiers already have it, why wouldn't the WG's weapons of mass destruction aka admirals have it? They are the WG's strongest military force for a reason.
And having a supreme grade blade (something Oden who was grouped with the great pirates) had not, on top of a top tier fruit, that's not half bad isn't it. Not to mention that the marines became much stronger under Akainu and that surely isn't due to filling up the lowest ranks.