I think you guys are hitting it right on the head. There are a couple of armies who easily deal with high toughness, Eldar, Dark Eldar, possibly Necron, and possibly GK.
Eldar have Shuriken Weapons which are devastating. If they are fielding small squads for Wave Serpent span Wraithknights are actually tougher, but if they are running footdar or larger squads of base troops its not a tough matchup.
Eldar can deal with them. Then again, they are nice to have when other Eldar bring their own Knights. Also, once a Serpent pops its shield, the Wraithknight has an easy kill.
Dark Eldar have Poison, blasters, and lots of it. Though due to meta shifts they aren't nearly as prevalent than they were in 5th.
Yup. They are scary for the Knight. Then again, my Eldar list also has 5 Serpents, 8 Spiders, and 2 Shadow Weavers to go along with two Knights. If I go first, there should be alot less to deal with on the field.
Necron have Wraith Span and Flyer Spam, one has the tools to take Wraithknights, the other can ignore them. Mind Shackle Scarabs are also supremely effective.
True.
MSS are bad. Wraiths aren't good. Knights are there to scare Anni Barges, take pot shots against flyers, and tie up Wraiths. Not ideal, but they certainly aren't useless here.
GK have Force Weapons. They have to rely on multiple sources of Hammerhand or Hammers to wound the Wraithknight, then Force Weapon Activation. Dreadknights are a hard counter, though they have their own difficulties facing Eldar. That being said, GK struggle to hurt Wraithknights outside of CC as even Psycannons struggle to wound them.
GK need either Hammers or a squad with attached characters. I barely see
MEQ GK to begin with, so stay away from
CC and take shots at those Pallies, vehicles, and Dredknights.
I think that many people who dislike the Wraithknight haven't seen it in action. I was initially underwhelmed, but once I used it a few times, I became a believer. Eldar, like many other Xenos, are an army of specialists. The Wraithknight is a generalist unit. You pay more in the context of the list, but it nicely fills some of the holes that Serpent reliant Eldar has.