To add my second comment (which I forgot to the first time round) I'll add a major factor to the fairness of the elves as my games against them have been fairly close run whilst using my beastmen. If anything I think my Averlanders would do better due to a more flexible approach.
If they do breed a sniper squad of stealth people that is fairly fluff suitable given that shadow warriors are the scout/sniper types for high elves and also the bows, even elven ones are all S3. Against a lot of warbands that means at best a 50% chance of wounding followed by a 33.3...% chance of taking them out permanently. We found that whilst the elves always hit even with hunting arrows for their heros they do have to come down/up and fight in order to secure objectives and fight the dreaded hordes of beastmen
(mostly T4 Gors so it becomes a 33.3...% chance of wounding) on anything like favorable terms (cue the two cornered shadow warriors squaring off against a minotaur incident)
The other point is always cost. Like the dwarves most other warbands should outnumber them and with some suitably tactical thinking be able to make that advantage work for you by snatching objectives, mobbing up or just giving them more targets than they can cope with. No one would think of going toe-to-toe with a specialist close combat warband so why start a firefight with the shadow warriors? Just get up close and mob them/hem them in/rip them limb for limb and sacrifice their souls to your chosen deity.
The warband I played against was one written from the annual and it didn't seem too bad.