I think overall the lists are very well balanced. Eldar have lots and lots of units, more than most other armies, which inevitably leads to huge variety in the comparisons made with respect to balance but I don't think much (if anything) needs to be done in terms of the overall power of the list.
Ulthwe do benefit a lot from SR5, but I actually like this distinction, what I have issue with is the 1+ initiative black guardians. That being said, black guardians can't take wraithguard or wraithlords so they are not too great deployed from a webway portal, which would otherwise be a great use of their 1+ retain. Likewise, using vampires negates their retain advantage. Also, the 4-strong aspect formation of NetEA Ulthwe is on the border of being not very useful, it is a totally different formation than in other Eldar lists. Six and eight are where it's at for me
I do like Warp Spiders, though I don't think they are categorically "the best" aspect. They are the best aspect when using a webway strategy, that is clear. When it comes to a mech strategy, for me that crown belongs to fire dragons, though dire avengers are also good. For air assaults, scorpions get a look in, as do shining spears because they give you an autarch on the board which is important to have with 2+ aircraft.
Avatar: this is a tough one to balance, for me it rarely actually does anything useful at all, and the situations where a FF drop is going to make any difference are pretty rare. In my games at least. In the end, anything at all will seem good when it is free
In my games, the Avatar is used mainly to synergise with guardians, i.e. gives them the option of being the first activation on a 1+, whilst giving them a unit to absorb the first hits and enough attacks to allow them to take on a wider variety of targets.
Firestorm: they're pretty good but I'm not convinced they're
too good. You need two formations of falcons to get enough - falcons are hardly useless, but it does act as a constraint on your army selection. Especially with NetEA fire prisms lacking AA.
Wraithguard: these totally transform guardians from being a formation that is only useful as a blitz guard into one that is able to assault. However that formation is 300 points, and you can only get three wraithguard, which means the formation is still vulnerable. Again, not convinced they are too good.
Phantom: this unit is poor, not enough attacks for a 750 point unit. TK is an improvement but not enough. Revenants are great, but holofields are not as great as they appear, quite easy to crossfire, break, and at 650 points they're expensive enough and almost always BTS. Better than 3 scorpions? Not so sure.
