What class 'only' loses 8%? It's not Rangers, for sure.
And given that 8% dps is about 4 times more than you get from basic +2 tome to +4 tome, and people grind for months for those even a 'mere' 8% is still cause for concern (read: nerdrage).
Whereas 1 AC is well... one AC. How much does 1 AC matter in Elite CO6? Answer: Somewhat, but not 8%, and while AC helps AC isn't the primary reason for bringing one. Even if the answer is 'very', losing a level 10 with no raid gear is what? One day off work?
Show me how you get a level 20 decked out in raid gear within one day of character creation and you'll have a valid point. Until then, you are wrong.