It wouldn't be too hard to name names among this group - the "restorers" include Hanse, Forse, Pritchard and maybe Spence. Foster, Silva and a few others would be on that list, but have plenty of new courses before undertaking restoration work.
Given that Gil Hanse did and does design some superior courses when given the chance to do new 18 hole courses (I haven't played new work of the other restoration specialists) I would take that as an indication that they probably have the talent to do it all, but chose, found, or were forced into a market niche of restoration. But, then, I look for the positive......
But, Mike is right in that routing is as different an animal to feature design or restoration as the long game is to putting. It could be quite possible for a gca to excel at one and stink at the other.
I like to think I have very few bad holes out there. I once spoke to a gca who lamented matter of factly that every one of his courses had a few bad holes. In his mind, he "couldn't avoid them." I shook my head because I think part of the battle starts with attitude and ends with never giving up on a routing or a hole design until I, as Tillie said, "beat sufficient character into the hole." Others would call it making lemonade out of lemons!
The post reminded me of the phrase, "A good collection of holes." Now, what does that mean, and can a good collection of holes not be a good golf course because they don't have a theme? I gather a well done replica course could go either way.