I think Teach is immensely more powerful than he's letting on, and is STILL trying to lay low, so the Marines don't address him as the actual threat he is.
I have two pieces of evidence for this. The first is Saint Shanks, the second is Rayleigh.
Saint Shanks has been a formidable fighter, Blackbeard injured him without his Devil Fruit, and Saint Shanks is explicit in stating "And it wasn't because I was careless."
This implies that Blackbeard straight up scarred Saint Shanks in a fair 1v1. Normally, the Teach we see is a sneaky backstabber.
But, his fight with Saint Shanks wasn't that. According to Saint Shanks, Blackbeard just overpowered him.
When have we seen that? There's still something more to Blackbeard. We've never seen him fight with his claws in a way that would be threatening to a character like Saint Shanks.
I think Teach has CoC, and is either hiding it, or is forced to manage it's use.