This is how every talent tree of every class fits into a pve raid.
In grouping, not all classes are similar. Some provide simple and easily defined benefits, while others provide auxiliary benefits beyond their basic stated role that more than make up for an apparent lack of output in that role. That was wordy, let's talk examples.
If your class can do many things, don't expect to be unqualified best at any of them.
There are three roles: tank, healer, damage (dps). But really, every class can do damage–you have to be able to put out some kind of damage in order to play the solo game. So it's really two specialized roles, plus the common role that everyone has. Some classes specialize completely in that common role: hunters, rogues, mages, warlocks. The rest can do multiple things, and this article concerns them.
No class is globally better at PvP than every other class. WoW PvP is a huge rock-paper-scissor game, where there's an answer for every move, or in WoW's case, Class A always feels overpowered to an opponent of Class B, Class B over Class C, and Class C over Class A. (except expanded out to an 11-way graph) While no class is universally dominant in PvP, some builds are universally better than other builds in that environment.
Your ability to solo partially determines the experience you'll have in groups. If you have an easy time in the leveling game, you are going to have a more difficult experience in the endgame/group game. The following list goes from easy-to-solo to hard-to-solo.