While mages with cure DO have a lot more survivability, I wouldn't really call them stronger than melee classes. If you do your best to avoid getting swamped by multiple monsters and just do boss FATEs when others are fighting it as well, you should do well on that front.

Also, I'd implore you to give marauder in dungeons a try. Tanking can be a lot of fun, and many players are quite understanding if you tell them you are new, and are open to suggestions. There's not many tanks in the game, so a lot of players are eager to coach and encourage new ones.