Actually, if DPS get ahead of you as a tank in this game, they get promoted to tank. Heck, sometimes it's the tank vs. the healer mashing sprint to see who can get to the mobs first. It's only really ever a problem if someone dies.

If you actually wanted a classical 'trinity design' where tanks are obligated to go ahead of the group and pull, then mobs would have to crit oneshot non-tanks. At the moment tanks are just melee dps with less rewarding rotations and lower damage output, in exchange for getting to do quicktime events when a tankbuster cast shows up every couple of minutes or so.