Of course some classes/specs are better than others at 1v1, but it would be incredibly easy for Blizzard to simply rank a 1v1 based on your class/spec (as in you are pitted against all random classes/specs, but you are only scored against how well others of the same class/spec do as you.)
Personally, I would love this and I think a lot of others would too, but I'm wondering why Blizzard has never implemented it. I'm thinking the reason is that they think from a psychological perspective that people will quit the game faster if they realize that they are not very good at PvP OR that it will alienate them from any sort of cooperative gameplay and hence quit the game sooner.