I don't see an issue. 1-50 doesn't teach you how to play a class. Your rotation, tools, and your class's identity doesn't come into its own till 60 anyway. So someone grunting through 50 levels isn't neccessarily going to be better than someone who doesn't. 60-70 is easily enough time and effort to teach someone how to tank. Its easy, throw your shield, axe, bubble or shoot at a target, AOE the group, and then just stay out of patches on the ground. There's the basics for tanking. Everything else is dungeon specific. And FATE grinding or level rouletting 50 levels doesn't help you with Nabriales, Nidhogg, or Shinryu anyway. Just gotta jump in and get your feet wet.
That could be just as easily a PLD, WAR, or DRK.
We all want DPS to have less queues with more tanks. Available, this is how its done.