Well, elves may only have fallen when they lost their gods, but what sort of empire was it? If it wasn't the sort of place that should have been supported because of the general misery it brought to most of the people who experienced it, like Tevinter could be argued to be, then maybe it's not the kind of place worth preserving.
Just because a place is great and powerful and looks all shiny on the surface doesn't mean it has a great excuse for existing. Another example might be the Inner Systems Alliance from Firefly.
To be honest , from what I gathered from codexes in DAI , I think the elven empire was the highlight of any magical empire.
Of course magic was great but it has its problem.
It seems the "Gods" (I believe they were individuals so good at magic , they became gods) held the whole thing with tyranny , law about magic reinforced by religious propaganda , and magical mind control.
It probably wasn't pretty ,but Mythal was keeping the peace and once she was murdered , things went downhill fast.
Again it's only theories but it seems your random elf if he/she was good enough could turn into a freaking dragon.Look at Thedas now and how people can barely deal with abominations.Now picture a dragon.
Also the tale of Ghilan'nain creating monsters left and right , (when she wasn't even a God) and Andruil forced to kill them all because they were threatening everyone.Even if it's not exactly what happened , it shows your random non godly elf causing trouble and a god has to stop it.
Anyway it seems when it comes to magic , elves were simply different back then and magic was everywhere.
Something happened , I assume someone put the veil in place and got rid of the Gods.
It created a whole new set of problems , of course.
But from what I can tell current Thedas is a better place.