You can also see that when an author becomes too famous and starts to ignore the editor(s), the books become heavy and repetitive. Editors are sharp. Trust them.
Fingers crossed I make it to the point where I have an editor =)
Definitely noticeable though, sometimes authors get too attached to the smell of their own farts to realize their writing is suffering under the weight of their own hubris.
And you're right, it's important to only take beta readers' opinions as just that, opinions. It is super helpful though to get their take, as I've been so close to the project where sometimes I can't see the forest for the trees.