Problem is that is the final MSQ dungeon with many new players going on and could be possibly matched with those at 450-470 IL.

You only need to take a look at Tales from the Duty Finder to know that people actually don't pick up their AF gear and run in rocking lvl 79 (if not even less) gear more then you would expect.

In a scenario where a tank is around 418 (in forgiven gear) and a dps (let's say BLM) is at 470 they'll be ripping aggro off much easier then the tank can keep up. It would make for an awful experience of aggro trying to pingpong around and would just be a bad run as a whole.