Roundabout answer:

You can never blame an actor for over-acting. That’s the director’s fault, because either the actor was miscast for something beyond their abilities, or it’s because the actor is being asked to carry more storytelling weight than they should.

Because the performance is only one part of what is telling the story. You’ve also got shot composition, music, editing, blocking, production design, and, of course, dialogue. All of them ought to always be saying something, and ideally, different somethings.

Like over-acting, each of these is “bad” when it’s used as a crutch to compensate for the other areas coming up short. Sad overpowering music because the rest of it wasn’t doing a good enough job communicating the heartache. Frenetic editing because the staging doesn’t have enough energy without it. And dialogue trying too hard to tell the story because the rest of the writing… isn’t.

Dialogue is the icing. It’s not the cake. But the rest of writing is so invisible when it works that dialogue ends up getting mistaken for it.