Once again - it's not KE specific. Warriors and Rogues also has builds which allows to do that. Moreother, such builds were possible in ANY Bioware RPG starting at least from BG2. Why KE should be treated differently from others? If powerplayers were asked for additional difficulty level instead, it would be much more reasonable.
If core class abilities (like barrier generation from damage) will be nerfed - it will be nerfed for all people and any difficulty, thus possibly making KE unplayable for average player.
Dude, I can be completely and totally unkillable in crappy treasure chest dropped gear at level 10-11 when I first get the KE spec. Try rolling a rogue/warrior/other mage spec and do that at level 11 and you're... well, not really that powerful. I'm not talking about only at level 21+. KE is that invincible from the very moment you get it. You can clear the entirety of the game with a single button if you want. No way in hell is that intended gameplay.
And I'm sorry, but if KE becomes unplayable for anyone with a nerf to the current barrier generation, they just plain suck ass and certainly aren't 'average players'. Those players should be playing on casual difficulty mode where anything and everything is easy to begin with.
Right now, KE spec is basically an extremely durable and potentially very high DPS class with zero drawbacks; AKA god-mode enabled gameplay on any difficulty. 
I managed to be kind of invincible with my two warriors. I only need two things: war cry and upgraded combat roll. I just roll away from most attacks, since the ones that hit hard have pretty long tells, and when they do hit me, well, some guard goes down. The horror!
See, right there! I wouldn't mind invincibility, but it would have to be because of the gamer, not a passive frikkin' skill that lets you facemurder Pride demons and Dragons on nightmare difficulty.
Rogues are powerful, but still have this nagging weakness that if they do get hit, they die. Warriors are powerful, but still have this weakness that if their Guard (which is massively inferior to barrier) fails or they fail to evade, they die. Tanks have this weakness that despite their inherent toughness, their damage is sub-par at best. Once again, I'm not talking level 21+ here, where any class is a god amongst men anyway. I'm talking about the core of the game that comes before that point.
I would utterly love to play a mage warrior hybrid class. But apparantly people who have no interest in playing an actual game and instead want what is essentially a glorified interactive movie, get to have their god-mode class. People who actually want to play the game at it's intended level of difficulty get screwed out of a very interesting class.
And once again, lowering the difficulty gets you the god-mode you want regardless of class. I can't exactly turn my difficulty higher then nightmare just to enjoy the game. People who'd want to be powerful would notice very little, if anything, from a nerf if they would just adjust their difficulty level. All the while people who want to play the spec with a challenge, could also get it. I really don't understand why people are against this. Nothing would change for the people that'd want to be powerful and everything would change for the people who'd want an actual challenge while playing a very interesting spec.