So Eldar have, imo, a fatal flaw when it comes to facing enemy snipers, and especially enemy rangers in an eldar mirror, and that is their inability to counter them outside of building their own rangers.
Take the Eldar v Eldar mirror for example. Imagine I build some rangers, and my enemy doesn't. There is almost nothing he will be able to do to touch my rangers unless I do something dumb, meanwhile, I will be bleeding him dry through attrition and running away. In fact, the only way for him to counter this is to build rangers of his own. This is really boring, and it makes rangers almost a necessity, whereas flexible builds are much more desirable.
Currently, snipers are the counter to every unit in the eldar Tier 1 roster, a critical faction flaw
I would make a few changes
1. Eldar rangers do not start with stealth by default, instead, it comes with an upgrade (to reduce the power of rangers in the eldar mirror)
2. An upgrade for another Eldar line unit to help them deal with snipers (either reapers or banshees)
-For reapers: Being hit by a sniper triggers some kind of counter attack from the reaper if he is setup (increased range, or special attack)
-For Banshees: Being hit by a sniper triggers a speed burst or stealth, allowing them to close the gap with the sniper
A new unit could help as well, but that probably isn't feasible before an expansion