Every one keeps crying about how broken this game is but all it really is is a matter of skill..
Healing: Every one keeps crying about op sorcs, but I've teams ruling ranked with merc healers and I can get my 5,5k hps with my scoundrel aswell.
DD: You can really play all DD's some might require some more skill in Yolos (Merc, Pt, Sniper) but if you have the "know-how" you'll be able to ppay each of them.
Tanks: The advantage of the Pt is the carbonize but else from that you just need to be able to guardswap (or you make the Sirox and outdps your DD's)