I don't think this is as black and white. You skill up by spending time with the domain. Of course, you learn better when you are involved in situations or jobs that actually matter. But getting rid of all the "mundane" distances you from the nitty-gritty and you lose that feel for the problem.

Right, there's a reason students that never dealt with a real problem, even when they get As, aren't as good as professionals. You need to do real work to get really good.