Ah, yes, because before that change, dungeons were a deeply engaging activity. /s
To me, the problem with the mobs is not the experience rewards they do or do not drop, but the fact that they are incredibly boring to fight. Attaching a reason to fight more of them does little to alleviate the feeling of tedium they induce. It helps suffer through it, but doesn't change the fact that it is just that. With the way most current dungeons are designed, it's not like there are mobs that can be skipped, anyway, so it's only a change that really affects the ARR and HW era dungeons.
In the end it all boils down to the issue that dungeons are not very engaging, so the sole reason to run them after the "new and shiny" factor wears off is the rewards. And the moment it is all about the rewards, players will of course optimise it to the nth degree. And I would argue dungeons suffer even there, as all that really can be done with them is the tomestone/exp grind. The only exceptions are at the very start of an expansion, where gear is a relevant iLevel stepping stone for a very short moment, and the improved iLevel for Ultimates one can get once dungeon gear reaches the ilevel synch of older Ultimate fights. In all other cases, the gear rewards are already irrelevant the moment a dungeon releases for an active player that does their weekly normal and alliance raids.
Of course, as most dungeons are all part of MSQ these days, there is zero chance of that ever changing, since they serve as a low-committment gear catchup mechanic and have to be beatable by everyone to not lock anyone out of the story, so there is no way for Square to improve any of this without alienating some players.
I am curious what the Criterion Dungeons will end up being and if they maybe can alleviate at least some of these issues. I am not getting my hopes up, though.