Well then its an extremely odd poll that I'm not interested in answering because I don't see how it has any bearing on how I plan to play.
Not that I am making a sorcerer tank, but yes you absolutely could. You can use summons to help hold aggro. Your summons could hold aggro on some mobs will you hold it on others, effectively holding them for your DPS better than a single Dragon Knight ever could. You could also wear heavy armor and use 1-handed with shield to get the tank skills from those weapon/armor sets. You could also use your knockbacks and CC to prevent any strays from getting to your ranged DPS back there.
Seriously...there may be certain classes that seem to naturally fit a certain role, but the whole point of this open class system is to not lock you in. You are supposed to be able to VIABLY play any role with any class. Did you see the video? A Templar Dual Wielding and using a Bow to do ranged DPS? Why wasn't he a healer?
Because he doesn't have to be!!!
Unlike your poll, the game is not trying to restrict my choices.