You are talking about the very best Glads here, I promise you that Holy Paladins are still viable, that they are under represented right now is no reason to not play one. The comps you are talking about have better synergy with other healers but many can be played with a Holy Paladin, especially melee comps.
There's a Korean team that plays on US servers and they got to like 2450 with Boomkin/Affliction Lock/Holy Pally
They do get farmed by anything with a spriest basically but, still very impressive.
That's the only holy pally that I've seen reach such a high rating this patch, but maybe it will be different in 5.3. It's almost like a whole new game for PvP. It'll be interesting to see.
I just don't see a holy pally getting Rank 1-5 over all at this current state.
Which means it will be even harder for a bot to get over 2200 in arena as a pally.
I still think Shams/Priests/Druids are in a better position than a holly pally, its just the current state of the game.
And if TuanHA where to ever make a Shaman CC, I will give him seem really good feedback on how to make the CC play like a 2.2k+ player. I know the class pretty decently and watch cdew stream a lot (considered one of the best resto shamans in the game)
Enhance... I'm not too sure about but, it doesn't seem that hard. It does looks fun to play though.
Edit: Since I will be switching to ret and possibly wasting all my conquest points on a ret set. How is it? I know the holy has always been amazing but, I never got to test the ret CC in MoP and there has been A LOT of changes since Cata lol