Seems pretty good to me. Great example of optimized detachments using appropriate craftworld traits.
Personally I'd prefer at least one unit of Wraithblades in trade for a Wraithlord. A unit with ghost swords provides quite a lot of attacks. Not sure what the overall wound potential looks like compared to the wraithlords in this configuration though.
If I were to try to keep the rest of the list as unchanged as possible, I could squeeze in 5 Wraithblades as follows:
-1 Wraithlord
-3 Dire Avengers
-1 Spiritseer
+5 Wraithblades
+1 Warlock
It's doable, but not advised. For th sake of simplicity, let's say that the available targets are either T4 3+ infantry or T7 3+ vehicles, whichever is more advantageous in the moment. If the Wraithblades have an ideal time, they get to charge a unit of Marines on their first turn, while the Warlock goes after a tank; between the psychic (assuming no DtW) and fight phases, they inflict and average of 7.99 wounds, paying 25.20 pts/wound.
To compare the opportunity cost of the units the Warlock and Wraithblades replaced, let's have the all the shuriken weapons shoot at the Marines while the Spiritseer and Wraithlord charge a tank. Those units inflict an average of 10.28 wounds, paying 21.79 pts/wound. In this case, I also didn't bother to charge with the Dire Avengers or the Spiritseer.
To be fair, if there were just Marines, the Wraithlord's Ghostglaive isn't nearly as useful. However, if we're being fair, we need to also consider the fact that the ranged output of the Wraithblades is non-existent, and the Warlock is using the crappy version of Smite (seriously, GW, why do Warlocks always suck?). Also, if there were just tanks, that Ghostglaive stays strong, and even the shuriken weapons stay relevant, but the damage output of the Wraithblades gets cut in half. Furthermore, since the charges would normally only happen on turn 2 or later, you really start missing the ranged damage from the replaced units. Speaking of multiple turns, one could always say that the Wraithblades could be pushed forward with Quicken, but remember that the Wraithlord has a faster base movement, and Quick/Restrain could be repositioning the Dire Avengers, rescuing the remaining Guardians, or slowing down incoming assault units.
Finally, with respect to durability, the trade is:
15 T6 3+ wounds
for
10 T8 3+ wounds, 3 T3 4+ wounds, and 2 T3 4++ wounds
This aspect is trickier because it varies a lot depending on the enemy's weapons, but considering how strength and toughness interact, I think I would rather have more S4 wounding the bulk of my units on 6s than on 5s, even if it means some of my units getting wounded on 3s by S4. Another consideration is that some mid-strength weapons do 2-3 wounds anyway. Such weapons have trouble getting better than 5+ to wound the Wraithlord, and the extra damage is largely wasted on the squishier models anyway.
Having said all of that, there's at least one style of list where I like massed Wraithblades. Take an Iyanden Battalion similar to the one above, then add a bunch of Wave Serpents carrying Wraithblades. Drop the Guardians on turn 1 or 2 as desired, but set up a turn 2 assault with the rest of your army. However, if I were to build that kind of list, I would consider putting the Guardians in the Serpents and drop Wraith
guard (with Wraithcannons) out of the webway. I don't like the idea of losing expensive models to the 1s I roll after my transports pop. Youight even consider making the little Wraiths Ulthwe to make them extra hard to kill.
