Again, I totally agree with you. In the end, it all depends on the individual. I don't say an artsman can't learn it at all. However, someone with aerospace background will definately catch stuff (ground school here) more easily than someone without a that kind of background. Let me give you and example. I did a course named "Introduction to Aircraft Performance" which explains how to analyse the performance of an aircraft by some datas. We saw, for example, how to determine the stall speed with/without power, gliding flight, climbing flight, vertical manoevers, range equations etc. All those things were seen pretty much in depth. The book we used is "An Introduction to Aircraft Performance" by Mario Asselin, a former CF AERE on the Hornet (If you can get a hold on this, do it, that's a very very interesting book). According to people I know very well that have done that course and that have done Moose Jaw say that what we see during this course is more advanced that MJ ground school. I really think that it gives at least a tiny advantage if the individual is bright enough not to sit on his butt and think he's a god.
Having said that, I don't think pilots with engineering background are better not at all. In the plane, individual qualities/learning skills will make the difference. In the cockpit and in the books are two very different things...
Cheers,
Max