Everyone has their own tastes, and I can see the aim of your scenario and would agree if we were in any other situation, but I think you’ve unfortunately managed to hit multiple night elf fan sore spots at once with this. I’ll try to elaborate on this POV.
It’s probably just the way this is phrased, but as it is, this sounds like you’re implying that both the night elves didn’t manage to retake Ashenvale - the only contested zone next to Darkshore where they could find Horde to attack - but that the Horde has managed to build non-military infrastructure there in the short time since the War of Thorns. Not a nice supposition for night elf fans.
The former setup (that this is going on in Ashenvale) robs these actions of the moral punch they really should have.
I don’t care if my neighbor is a great friendly tauren, if he’s sitting in -my- house, sipping -my- coffee out of the skull mug his buddies made out of my siblings that they killed on the way to steal that coffee, I won’t particularly care that he himself wasn’t involved in the invasion or murder - I’ll be angry just the same that he’s enjoying the spoils from them.
If you mean for the night elves to push through Ashenvale and the military there, and then start raiding civilian locations in the Barrens, that would be a different story. Though, unfortunately, after all the visible Horde citizens’ support for the War of Thorns and killing night elf civilians in their own home, I don’t think that many Alliance would see a mirror as an unspeakable action - after all, the Alliance was just told to forgive the Horde for that without even requiring an apology. (This mindset is a big part of why I think the War of Thorns was such a stupid escalation to put in the game.)
Again, this would be perfectly fine - even commendable - in most scenarios, but coming off the tail end of BfA… “Why should the Alliance be so quick to condemn their own when it took Horde leaders multiple patches to even make a peep about how maybe burning thousand of civilian elves alive might not be very nice? And then they just swept it under the rug, so purposefully killing civilians of the other faction apparently isn’t bad enough to require apologies by the Horde’s precedent.”
I don’t agree with the logic of that argument, but it’d become yet another case where the story is asking the Alliance to bottle up their feelings (which the story itself just whipped up to a frenzy) and set aside their emotional enjoyment of the game so that the H/A status quo can continue. It’s not a way to foster good player relationships.
Though that just means that it’s Elune getting villain-batted rather than Tyrande getting villain-batted. I don’t think either option is really great right now.
Overall, I think that the problem is that the Burning of Teldrassil so -stupidly- upped the stakes that a simpler scenario like this cannot compare with it.