The problem doesn't lie with tank design. If anything tanks need to understand the fight more then anyone in order to appropriately position the boss and use the required cooldowns on the queue or see themselves or someone else go splat, that goes especially in Ultimates. Aggro management is a design that just isn't enjoyable, I did not feel enjoyment when successfully stance dancing or gambling if some dps is going to crit or not.
DPS is much more lenient and the problem lies there, people will at most scoff if a litany or trick attack is out of sync. The dps role is very forgiving in the community and that's where the problem lies as to "why there is a shortage of tanks" and an equal if not more shortage of healers.
An underperforming dps is just that, doing less DPS. And sometimes when you are in that one group as a tank where you are dishing out enough dmg to be competitive with the dps you start to wonder why you don't just swap to a dps and your life will be a lot less stressful when you ask yourself the question, "will there be enough dps to kill the boss".
I'd like to see the developers put more of a strain on the dps with dps exclusive mechanics and then you'll naturally see players trickling to different roles.
