Honestly now, if we had 8 variations of tanks and 2 for dps it wouldn't matter dps would still have more players. Tanking has a lot of responsibility that most players just dont want to deal with. Tanking is also pretty boring for most people, and if you try to make it fun or more DPS like, people seem to feel like it should be able to be considered dps(war) even if its intended as a tank. Adding a tank will just have people who already tank decide which is better or more fun. But it wont cause a big increase if any in the tank population. Adding a DPS could bring more players in or people would just switch mains. But DPS players are highly unlikely to just switch roles. Lack of tanks will always be a problem no matter how many tank jobs there are.
Even though I love DRK, NIN,THF,SAM, if they were tank classes unless they were just absolutely amazingly super fun its very unlikely i'll use them in group content. I even have my paladin at 50. But I have no real plans to main a tank in content, as frankly holding hate and taking damage, while giving my living or dying full reliance to others isn't fun for me.
There are plenty of reasons why having a few tanking classes, lots of DPS, and a few healers is pretty normal across RPGs and MMORPG's. You'd be hard pressed to find tons and tons of people who'd rather get hit by monsters and players rather than being the one doing the hitting.
Even harder pressed to find people who don't mind being yelled at for something they didn't do after a group dies or a duty fails. Blame the tank, Blame the healer. That's why these classes lack players. Its always their fault even when it isn't. They even have to learn more about content and the mechanics they'll deal with over DPS.
