Only mongoloids play double healer teams. Most of them are like 2.5K at best playing other comps, and then they get 2.7k+ playing double healer haha. It's fucking hilarious how it doesn't really matter how many mistakes they make because they have enough healing and CDs to rotate through that it doesn't make a difference if they blow an extra CD or two by mistake.
Also it's disgusting how blizzard can just accept this comp, it's clearly broken and allows very bad players to get much higher ratings than they should have (much more so than any 2dps+healer comp does). Someone mentioned LSD, but against a bad LSD you can just kill them straight of the bat, you don't have to wait 10 minutes until it's even possible to get a kill and then you still might lose just because the rogue has worn your team out of CDs, without requiring any sort of skill.
The comp slowly kills the game, sure those who are queuing it might enjoy it for the extra rating, but everyone they meet absolutely loathes facing it and are thus much more likely to quit the game.
It can't be that hard for blizzard to just launch a really small patch (or even a hotfix, although that would probably lead to minor client bugs) so that you can't queue if more than 1 player on your team has chosen the healer role, also they would have to force you to join as a spec that fulfills that role just like in bgs.
Double healer is hardly a new thing. It's been around since Wrath at least and probably before then too. If they were gona do something about it they would've done it by now. Wouldn't say it was any easier in Wotlk to win with double healer than with LSD, and it's probably the same story now: there will always be some comps that are easier to be successful with than others.