Some of the balance issues relate to DB generating spells, which would not be affected by the QU penalty of armor. . .
AT 1 with bonus DB balances to armor.
AT 20 with bonus DB becomes rather nasty, few characters have much non parry DB in AT20.
I beleive the hyperbole filled reference I've seen tossed around is:
"I don't want to see an AT20 wearing, invisible, silent, flying caster blasting people with lightningbolts."
Which actually can be a lot of fun in a high end game, but usually that kind of thing is a bad sign.
I suspect it's a bad sign mostly because it's an archetype issue, strong archetypes force specialization of strengths and weaknesses, which prompts association and party formation. . .games that stress archetypes tend to have stronger party concepts, games where 1 character can do everything well tend to have weak party concepts. . .any group can form a party on a roleplay basis, but people tend to find reasons to get along when they need each other, and find reasons not to get along if they don't need each other. . .how many games on all systems crash on the rock of that one all around mighty character who no longer needs the others (or think they don't)?
Strong archetypes are not necissary, just helpful to keep the game moving, some groups can get by without them, some groups need them to prompt party co-dependant behavior. Mostly this sort of thing matters as to what style of game you want to run.