First, no one has yet soloed the game with a rogue. There's one person I know who's trying, and is uploading the results to youtube, but they haven't gotten their first ally yet.
Secondly, mages are powerful in the game. They're powerful in the lore and BioWare developers themselves have said that it's accepted around the office that mages are the most powerful class. (This was stated on a thread about increasing mage's power because they were too weak) Mages only need to pump two stats. Mages can take mana potions while melee classes do not get stamina potions. Mages have spells for crowd control, AOE damage, defense, single mob offense, etc, and a specialization that lets them wear the best armors in the game.