I would like to discus the Meta Mechanics of pve. There are different ways apply a meta in a MMORPG, for example:
WoW: establishes their Meta through each content patch. Changing best top dps classes, changing best healers and best tanks with each patch.
Star wars the old republic: there are best classes for constant dps, constant healing, burst healing, burst dps, HoT, DoT, etc. So in other ways the best classes depends on the boss mechanics (constant damage received by the party, burst damage received by the party, intermittent damage dealing to the boss, etc.).
Guild wars 2: best classes depends exclusively on the raid mechanics. For example, when the boss reduce healing of the party the best healer is the Guardian because he can heal and prevent damage so the healing debuff doesn't affect his damage prevention.
I think best way to establish a Meta is how SWTOR and GW2 are established.