WotC asked for feedback. It's not INTERNET RAGE to give them that feedback.
This is literally a question WotC has provoked, intentionally, to see if something works. Telling them it doesn't work like that is valid, useful, and, indeed, part of what we should be doing as a community.
If something sucks, we can say it sucks. Let people have their opinions on the thing people were asked their opinions on.
And, IMO, it does suck. It's not what I want out of a purple dragon knight any more than "brutal, fiend-worshipping madmen" is what out I want out of a kender. Yeah, you probably can justify it in the lore, if you control the lore, but it's more about missing the opportunity for a cool kind of character that's already right there. Just, frickin', do the cool thing that it already is.
Sorry if that opinion hurts the feelings of a WotC designer or whatever, but they can also pick their battles, and they don't really have to pick this one.