if you run the wraith formation its awfully nasty.
they get battle focus, and then sure 6" and then kill everything flamer... ughh
but if you use Wraithguards, you just auto kill it, more or less. with the S: D crap
The Iyanden codex already meant you could battle focus and run 6" with a kill everything flamer -5 x st4, ap2 with instant death/autopen on 6's was already nasty.
Wraithguard don't fit in falcons, so the only ways they can get to you are either a wave serpent in which case you can try to take it out before it gets to you and there can be no more than 5 of them, or they footslog and they aren't a threat for a couple of turns.
Big squads of them are 300pts+ so bar a full wraith list you won't see that many of them.
Apart from the wraithknight changes, the rest of the wraithstuff isn't that different.
My ten wraithguard have always killed whatever they shot at, including greater demons, primarchs and spartans
Heldrakes, Baal preds, plasma - anything ap3 and high enough strength will still kill wrathguard. If they get close, charge them with a throwaway squad, then charge with a dreadnought or a character. That ties them up for the rest of the game. Fearless means they can't leave cc once they're in it.
Wraithblades with swords lose to anything like monstrous creatures and dreads and I'd charge the axes with a blob squad - if they get charged, its one attack each for them which should tie them up indefinitely.
Of course, if you fight someone using dark eldar allies with a webway portal then that's different. But even then, its a 400+ point unit being used to kill one thing. Unless you have a super heavy worth more, that unit will never make its points back.
The main thing is try fighting them and make sure you know the eldar rules. Eldar win through special rules people either forget or don't know about. Its why non eldar players tend to hate them.
Things like 'warp spiders can teleport after you declare you're going to shoot them' will waste important shooting. Its not so bad if you know about it, but when you decide to flamer them rather than another unit because you didn't know or forgot, its either suck it up and grind your teeth or start an argument about how 'you wouldn't have done it if you'd known'
It won't be a fun game after that.
I compromise - I tell my opponents about what beardy eldar units do before the game rather than saying mid-game 'excuse me, just to let you know, if you shoot those spiders, I'll just teleport away so you'd be better to shoot this other unit over here' because I would still like to win, rather than playing both sides