As for that, it's simply not true. I remember the leveling dungeons in WoW, which are equivalent to roulettes in FF. The tank's pull was completely ignored because between group stuns, classes with super-effective off-tanks, defensive CDs that each class has, and summons that many DPS can use to taunt, it was a game where you could really do without the tank. In fact, there was a whole period where a friend and I had fun doing dungeons together. DPS-heal, or even DPS-DPS (with a druid just in case), the tank wasn't really useful. You mention arm's length, which is pretty much the only defensive tool available to most classes in FF. In WoW, even many pure DPS classes have several defensive tools at their disposal. Special mention goes to the rogue.
In FFXIV, classes are remarkably confined to their roles. It's a very (too?) rigid game in that regard