Law not having CoC proves you can be a 3 billion tier without CoC so long as you are a DF merchant
However to be a 4 bil or 5 bil tier you need CoC from everything we have seen. All the pre skip yonko had CoC. WB had one of the strongest DFs and he still had CoC.
So at the very least we can say Akainu probably has CoC. Maybe Kuzan, as he was a fleet admiral candidate.
We all know Law's 3 billion bounty is BS, so lets ignore him for the time being. Even if his bounty is well deserved, bro's nowhere near a top-tier, so we can't take him as a proof of anything. He certainly has top-tier potential even without having CoC though.
All admirals not confirmed CoC or CoC coating users, Big Mom isn't that great a CoC user although she does have it. Their existence alone is more than enough to confirm non-CoC coating users can reach the top. The discussion is about whether someone can do it without CoC coating or a DF, the answer so far is a no as there's no confirmed top-tier that doesn't have a DF or CoC coating.
We do have CoC coating users who can still fight at top-tier level without using CoC, but we don't have a pure non-CoC coating user who managed to make himself a top-tier without a DF. If Gaban did that, then he'd be the rarest of the rare case.