I have read quite a few of WoW’s books. I would argue that A Good War and Elegy had the best portrayal of the night elves in years, because a Good War showed just how much work the Horde actually had to put in to get through Ashenvale after their initial ambush, with their advance stopping dead wherever Malfurion showed up, to Elegy showing that despite knowing they weren’t going to hold the line forever, the Horde will pay for every foot of ground they take.
Up until the very wend where Blizzard went full MoP 2: Undead Gigolo and had the tree torched, the night elves I would say where shown to be pretty good.
But the problem isn’t that the night elves can’t take on the the Horde alone. The problem is they are always the one having to fight a losing battle and is in desperate need of rescue. They are always the one who is caught off guard, taking heavy losses and losing most of their territory until someone comes in to rescue them.
Meanwhile we have races like the Forsaken running train all over northern Eastern Kingdoms since Cataclysm with minimal help from the bulk of the Horde’s forces. The rest of the Alliance are able to go out and and attack the Horde in the Barrens and are able to defend their homelands without much issue.
But the night elves are apparently taking on 90% of the Horde all the time, with little to no help from the East, and their plot significance to their own faction is usually summed up as “Horde is attacking us again, send help.”