Grey terminal wasn’t about ace but there was a coc moment for him there. If Oda wanted to show it, he’d have shown it so the question is why. It’s not like there weren’t any fodders around him at any point there were fodders near him to knock out at lots of opportunity. And we can tell that his physicals have more or less peaked because whenever people in verse mention his growth it’s his devil fruits that are getting stronger never his haki.
As I said, Oda is just writing Blackbeard different for now. I’m not saying it’s impossible for BB to use CoC in the future, just as of right now I think oda is purposefully not because he has BB going a route opposite his father. Amassing devil fruits and using those to get stronger since fruit powers are what defeated Xebec.