"clue-less": without any clues about the workings and mis-workings (parts to stay away from) of XAML/WPF...

Clues come from experience. And without experience, just starting out on a subject, makes you clueless about it.

While they may be technically correct, words like "clueless", "naive", or "ignorant" can be really aggressive and feel like ad-hominem.

A more constructive phrasing might have been:

The majority of people that I've heard criticize XAML are people who are just starting out with it and don't fully understand what it has to offer