The thing is that the future king of Britain WAS in fact married to a girl who, according to your definition, was arguably even more aristocratic than the prince of Wales himself. If you would compare Diana Spencer's family tree to that of Charles, you'd find that she's related to more English kings than even Charles is!
Yet that very fact didn't prevent their marriage from eventually braking down. Or for example, princess Irene of the Netherlands who married the very royal Carlos Hugo de Bourbon Parma. Ended in divorce.
Contrast that with the by all appearances extremely successful union of King Carl Gustaf of Sweden. Queen Silvia of Sweden was a commoner until at least age 30, yet I'd have a hard time pointing out a royal consort who's better suited to her place in the fold than Silvia is.
I don't think this has anything to do whatsoever with the Swedish concept of monarchy--Silvia would in my opinion have done equally well in, say, Britain.
That said I don't necessarily disagree with you on the whole, because in a way it would diminish the overall perceived 'specialness' of the group of people we call royals. All the same, judging from what I see in the media, the job of royal consort isn't exactly rocket science. Neither is it on the scale of, say, running a global business like, for example, General Motors. The skill set it requires seems to come down to a combination of that of a Diplomat/PR-Spokesperson or politician/Social Worker. Having clean-cut looks and an interest in fellow human beings is also a requirement. Depending on the country, it would also help to have some sort of strategic vision of where you think your country should be headed, but necessary it ain't.
Now, in my view, there are millions of people who could, with some training, fit those job requirements with relative ease.
Don't forget that most of these royals have tons of help: assistants who organize your calendar, ghost writers to pen that witty-and-wise speech, stylists to put together outfits that convey thoughtfulness for the assignment while cutting a good picture, etc.
Sometimes one can wonder how much these royals actually figured out for themselves! This is why 'morganatic' marriages according to the 'German' definition, can work just fine. Question is: Do royal 'delegates', as in, 'the people', buy into whichever commoner grabs the scepter, and will they indefinitely?