What is wrong with cone aoe?

[Deceptus]

In addition, because Squeenix is allergic to mobs sharing the same physical space, they'll keep dancing around and adjusting themselves - meaning that nice tidy pack you got clumped up for your conal Overpower has now done the shimmy-shimmy and some of those mobs are now outside your Overpower's damage range.

This is the right answer. It's a repercussion of SE's insistence on making dungeon mobs HUGE.

Unless you were routinely screwing over your casters by standing in the middle of the mobs despite even the circular AoEs reaching all mobs from the pack's edge, nothing was changed.

See above. Many times it wasn't the tank moving the mobs, but the mobs deciding they were going to move on their own to a tanks flank.