The Eldar have become hyper-specialized to the point of uselessness
I've heard the arguments, I know, I know. "Eldar don't win slugfests." "Eldar score on secondaries." "Eldar are a glass cannon." "Eldar have a high skill floor." "Eldar take effort to learn."
Blah blah blah blah blah.
While all these are very well and good in principle, in practice we have to acknowledge that the rules GW gives for it are horribly executed. The idea of a glass cannon army makes perfect sense... but is so poorly implemented in the way 40k's (already bloated and convoluted) rule system tries to realize that idea, that it just plain fails on the actual tabletop.
And I don't think it's down to malice or GW "hating" eldar, they've just become so obsessed with making every faction "unique" that they've whittled away every aspect of the eldar that doesn't revolve around "go fast." Because "go fast" is our faction's specialty, just like "numbers" is for Orks, Guard, and Tyranids, "tanky" is for Necrons and Death Guard, "shooty" is for T'au and Votann, and "generalist" is for Marines.
Which is theoretically fine, but at this point it's left the army with no actual tools, abilities, or strengths beyond "runs really fast." They got so lost in trying to give us a "unique identity" they forgot that identity has to be functional at the end of the day.
I'm not going to respond to comments on this BTW.