So I've been playing SWTOR all weekend, 3 characters up to level 11 and another 2 up to level 5. And while the primary purpose of that was to find out what classes I would like to play at release, I was also thinking about class balance, because that tends to be a thorny issue with this sort of game. First of all it has to be said that the class balance between the two factions is perfect, for the same reason as the balance between white and black in chess is perfect: The classes on each side are mirror images. While let's say the Sith Inquisitor is hurling lightning, and the Jedi Consular is hurling rocks, that difference is purely cosmetic. The Force Shock and Force Lightning spells of the Inquisitor work EXACTLY like the telekinesis variant of the Consular, having the same cost, damage, and effect.
That leaves us with only 4 main classes, each of which has 2 advanced classes. As you only play the main class up to level 10, and up to that point they are all solo dps classes, we need to look at the 8 advanced classes. Group size in SWTOR is 4, so presumably we need 1 tank, 1 healer, and 2 dps. Of the 8 classes there are 3 tanks, 3 healers, and 2 pure dps, so at first look it seems that there shouldn't be a tank/healer shortage. But on second look all 8 classes are damage dealing classes, at least it says so in their description, and the 3 tank classes and 3 healer classes are hybrids. Of the 3 talent trees every class gets, it appears that only 1 tree per hybrid is for healing or tanking, while the other 2 are for damage.
So in the unlikely case that every class and talent tree is equally popular, we end up with 3 tanks, 3 healers, and 18 damage dealers. And it is likely that there will be even more players going for the damage dealing talents instead for healing and tanking, based on the experience with other games of this kind. Fortunately every class has a self-heal out of combat, but shortages of tanks and healers in combat are foreseeable. Who makes a Sith Sorcerer to then spec him as healer? The problem is aggravated by the apparent lack of a dual-spec feature in the release version, although it is said that this feature will be added later. I think it will be very needed.