The issue with DPS vrs Healer/Tanks is that people do not want to play healer/tanks as they get made good targets for harassment if things go astray. From reading what people have said in the forums about tanking/healing, they are afraid of the lash back they might get if they mess up. But honestly, I've only had two people lash at me for minor mistakes, all my major mistakes that cause wipes have led to people giving me really useful tips. Tanks already have mounts you can get from queuing up as tanks for dungeons, so there are some already in place. It's just the lack of interest from either people who do not like the play-style, or those who are afraid of actually trying because they don't want the heat of possible harassment. Even if it's very rare to happen. At least, from my experience.