Spiking one target isn't that much in order in pve, having your party attack the same target is more. But with henchies that is not a problem, hehe.
Typically in one area of the game will have counters versus certain things. Like foes using ward vs elements in certain parts, stances in others. Making other classes more effecient at different stages of the game.
Take mesmers for instance. At the start of the game the total hp of monsters is low enough for conjure phantasm to kill stuff in a few seconds. As the hp of the monsters grow this becomes a less efficient way of killing stuff, so a warrior wil be able to smash thing much quicker. Elementalists get much added power for their attributes and by then they will also outdamage the mesmer. For this part of the game the mesmer needs to become more a support char, interrupting, hexing. Mostly conditional damage tho (high dmg on spellcasters with backfire).
Towards the end the hp of monsters is huge, but so are their armor levels. The warrior and elementalist suddenly have difficulty maintaining their damage (as far as elementalists go the most popular one, fire, has the most difficulties here as the monsters are strong against it). A mesmer however has armor penetrating spells, energy burn on a mid-level monster is outdamaged by what others can do, but on the end level parties tend to start to ask for domination 'nukers'.
So really, every class is good, it's just what you prefer. You'll be needing to adept to different areas anyway
