A few days ago I did some arena, I played 22 games 20 of which were against hunter teams. I played against Hunter / Ret, Hunter / Warrior, Hunter / Rogue, Hunter / DK, Hunter / Feral, Hunter / Spriest, and Hunter / Mage.
MLS can be quite good, but it's insanely spec dependent for the Warlock, you basically have to be right spec, gems, reforges etc vs teams or you pretty much zone in and are gonna lose or time out, and honestly most of the high Mage / Lock teams atm is just to do with Fire which I think everyone is expecting to get nerfed. Spriest / Mage is still infinitely stronger and even with Gateway being extremely easy to spam at the moment, you often barely can beat cleave teams who never target anything except one person the entire game and just walk at them back and forth across the map. Without gate there are plenty of teams you just lose to by default, and that's just going to be the case in every game next patch without some pretty major changes to compensate imo.
Also good to keep in mind that the changes to BEA and Dalaran are also going to significantly hurt Warlocks (not saying they shouldn't be done - there are too many knock offs atm) and Dalaran is probably going to be near impossible against cleave teams since you can't get a decent gateway on that map and there won't be a second level.
There are a few Warlocks who do well, and almost exclusively as Destruction, I haven't ran into a single Demonology Warlock, and have fought maybe one Affliction Warlock in all my games at high ratings this season whereas I literally see dozens and dozens of people of the various strong classes atm that I've never even heard of etc so I don't really think it's comparable.