You may be right. The developer does, objectively, write good code. Was it so much better than the old code that it was a worthwhile endeavor? That is debatable. Some of it was style change, some of it was idiomatic changes. There was, as far as I know, no performance change or refactoring that eased code maintenance or anything like that.

Rather than being a "bad dev" he may be simply a "bad value" -- good, but not worth the pain.