Cleaves too dominant in Arenas
We think cleave teams are too dominant, especially in 2s. We don't think they are as bad in 3s, but the community is very focused on 2s at the moment.
We don't think it's as simple as melee classes doing too much damage or having too much armor. We don't even necessarily think it's "melee" because I'm not convinced shamans and druids are affected. We think it has more to do with ranged classes not always able to bring their CC or survival tools to bear against melee.
Keep in mind when you are talking about Arena comps, the issue isn't as simple as saying that X beats Y. Often it's a question of who you want on your team. To take just one example, we think that last season if you were trying to decide between a hunter and warrior, the hunter brought a lot more to the table. There was no benefit to be gained from taking a warrior instead. There were a lot of reasons for this, but one of them was that physical damage just wasn't that useful and another was that warriors could never keep on a target. Another was that DKs and paladins dominated smaller brackets. In this season you can make the argument that warriors are more attractive than hunters. One of the things that a hunter could theoretically bring -- stronger CC in the form of traps -- may not be useful enough compared to say the CC you could get from a mage. This has almost nothing to do with warriors beating hunters in 1v1 duel situations and everything to do with how you want to build your team.
Obviously (I hope) I am boiling down a complicated situation to a simplistic level for purposes of illustration. My point is that often, in our minds, it's rarely as simple as "If my class did more damage, my class would be at 10% Arena representation."
Plate Armor vs. Cloth
I think you are just looking at the armor number and assuming that translates to survivability. A lot of the damage done, some even from plate wearers, is not physical. Plate-wearers are by and large melee while cloth-wearers are by and large ranged. If you're a caster, not only are you doing ranged damage but you're punching right through the armor anyway. All the casters have spells that increase their mitigation far beyond the simple armor number on their cloth.
I think a lot of the arguments you see on the forums right now about melee > ranged are simplistic. The armor on plate probably has an effect, but I don't think it's the main effect. Consider the rock-paper-scissors of a generic melee class to a generic caster class. The balance is supposed to be that the caster can cause damage at range. The melee class can attempt to close to do damage, but the caster has crowd control and escape mechanisms to get away. Now consider that most of the caster crowd control and some escape mechanisms are magic, which can be dispelled, while the snares, stuns and charges from melee are often physical or can't be dispelled at all. From that POV, you could argue that dispels and Blessing of Freedom in particular, are far more destabilizing to Arena balance than just plate.
New post, concerning Ghostcrawler's use of 'cleave' when talking about 2s:
Regardless, we do think certain types of melee are too well represented especially in the 2s bracket. We don't think this is a fundamental flaw with how casting works. We just think the caster escape mechanisms can't trump the melee closing mechanisms, which they need to sometimes.