Trooper healing is much more difficult/shitty because of ammo management (the more you heal, the less ammo you have. the less ammo you have, the slower ammo regens. Heal too much and you are fucked) They are pretty much a dead class at 55.
Trooper dps is behind several others, and you don't get the raid damage reduction bubble ops get or the raid damage buff (bloodlust) marauders get. You get exactly 0 burst damage cooldowns. At least you can cure yourself, I guess? And you don't have to worry about a bunch of buffs/debuffs or other bullshit, it's a pure whack-a-mole priority rotation that screams "Macro me."
Trooper tanking - not sure, but seems fine. Doesn't apply to me because I'm a mercenary.
That said, unless you are doing hard/nightmare raids I'm sure you can do fine as a tank/dps. But I wouldn't play a healer. The resource system completely fucks you. But I certainly enjoy my mercenary because blowing shit up with guns and missiles feels cooler than chopping at things with swords or magic for the billionth time.
Another thing to consider is stealth. Holy fuck do I wish I had stealth. This game throws hordes, and I do mean HORDES of worthless trash at you while you are soloing. And in a dungeon one stealther in a group makes a huge difference because they can CC things without aggro so the rest of the group can sneak past.