I think no large games use an engine as-is, they will always extend and change it in some ways to make it fit their game. Besides the question was not about AA/AAA games. Unity also did not fill that segment. The question was whether Godot will be able to fill the space Unity has. And I don't think it can currently. But with more development it definitely could. The last time I used unity I was very appalled by how bad it actually was, I admit this is something like 5 years ago but I doubt it has changed.