If you enforce M/C/H I think these specs and probably every hybrid aside from Shadow Priests would largely disappear from competitive arena. I never said that one grandmaster MCH comp would surface -- that's ridiculous. People play a wide variety of classes so just because RLS might be the best MCH in our hypothetical scenario, it wouldn't mean mages disappear because a lot of good players play mages and they would be fine running RMP or WMP or whathaveyou. But to me MCH would totally fuck with comp diversity. What would a ret paladin run under that system? Ret/Moonkin/Healer? No, it would HAVE to be Ret/Warlock or Ret/Mage (and even those would be shit). A ret paladin would not benefit from partnering with the third or fourth caster on the depth chart -- they would naturally gravitate toward the best casters. This has historically been mages and warlocks, and that's why I think enforcing MCH would have a negative impact on this game's fun factor for about 50% of the games classes. And to be honest WoW arena can't afford to lose any more fun factor at this point.
just stop and go back to GW2