This is likely a stupid question, but this is the place for those, right? 
In the TLP world (in your opinion), with no intention of taking part in raid content, around what expansion do you think that a Trio, would absolutely need a tank, in order to effectively enjoy the majority of it's content? (Before Mercs)
A little theory crafting is appreciated, because the more I think about it the more I am leaning towards a (Shaman, Mage, Necro) or (Shaman, Mage, Chanter) trio...
With Shaman debuffs, mage pet-tanking, a third caster could be much of anything. And in that case, why not just make it a tank(y) class?
For example: (SK, Shaman, Mage) or even (Bard, Shaman, Mage)...
I know that most of these sorts of class composition questions/answers are self-masturbatory, if not entirely moot.
But I wouldn't mind if someone changed my mind. As a matter of fact, I would love it if someone managed to.

In the TLP world (in your opinion), with no intention of taking part in raid content, around what expansion do you think that a Trio, would absolutely need a tank, in order to effectively enjoy the majority of it's content? (Before Mercs)
A little theory crafting is appreciated, because the more I think about it the more I am leaning towards a (Shaman, Mage, Necro) or (Shaman, Mage, Chanter) trio...
With Shaman debuffs, mage pet-tanking, a third caster could be much of anything. And in that case, why not just make it a tank(y) class?
For example: (SK, Shaman, Mage) or even (Bard, Shaman, Mage)...
I know that most of these sorts of class composition questions/answers are self-masturbatory, if not entirely moot.
But I wouldn't mind if someone changed my mind. As a matter of fact, I would love it if someone managed to.