Both yes and no. At low rating, what you say is absolutely correct, but at high rating the representation of the class matters much less than the strength of the class. It still matters, just not as much.
So really what we're looking for a strong upward trend from global representation to high rating representation. So if we go to somewhere like World of Wargraphs (other sites tell a similar story) we see this:
Code:
Class / Spec % (2200+) % (Global)
Arms Warrior 23.7% 3.5%
Frost Mage 10.9% 4%
Restoration Shaman 9.9% 3.1%
3.5% is the popularity of Arms Warriors. 23.7% is how good they are at high rating. That is to say, Warriors are overrepresented in high-end arena, being 6-7 times more common than the popularity of the class itself would suggest.
If that isn't a problem, then I don't know is.
Like I said, there are no two ways about this. Nerf Warriors, and fast. They are totally and utterly out of control.
Frost Mages and Restoration Shamans are also running amok, clearly, but they are nowhere near Warriors. As someone just pointed out, Warriors just eclipsed S5 DK's at the most overrepresented spec in the history of the game. It is literally ruining the season.