Varian participated in it, but not as a deliberate show of solidarity IIRC. He was just there at the time. I also don’t consider the contribution of irregulars to be a direct contribution of forces as the landing of troops in Darkshore for deployment in Ashenvale would be.
The Barrens I look at more cynically. It appears to have been something done to expand Theramore’s power base, and to colonize the area - not expressly to help the Night Elves - and were I to be even more cynical, I would ask why Stormwind is building a logistical dagger to the Night Elves’ underbelly in Ashenvale. Why they’re favoring a port that the Night Elves can’t interfere with. Machiavelli had a few things to say about this kind of thing.
Keep in mind, during this time, the Night Elves WERE directly contributing forces to Stormwind’s defense. They did it in Vash’ir, which, if it fell, would have, in the words of the troops on the dock, meant the end of Stormwind.
Varian also failed to dismantle the Horde, and while doing so, he strongarmed Tyrande into giving up Azshara under the assumption that this would lead to peace. We can see how that turned out. How many of those super-long range nuclear catapults were built from wood culled from that region? The world may never know.
Then after Teldrassil, Anduin refused time and time again to fulfill the obligations that members of the Alliance have towards each other - protecting the core territories and the people who live there being at the top of that list. Troops could have been funneled through those portals, giving the Night Elf military that extra bit of time they needed to land. But Stormwind contributed nothing in the way of military assistance during the conflict - which is kind of notable when we start to think about how things may have been different if Anduin, Genn, Tyrande, and Jaina were on the ground during that invasion, along with a battalion or two of Stormwind troops. Instead, Anduin diverts all efforts to the seizure of Stormwind’s geopolitical interests - like Lordaeron, Arathi, Kul’Tiras, and Zandalar - including the diversion of the Night Elf military. Then when the time comes for Stormwind to honor its commitments as an Alliance member, Anduin refuses. He not only wants to destroy Zandalar’s navy (something that now is in his power), he wants to invade their capitol to make a point, even though with no navy, he could have just bypassed them.
Anduin caps this off with a “peace treaty” that fails to address the reasons the Horde went to war in the first place, and leaves the Night Elves dealing with a historically volatile and genocidal power in their immediate vicinity. He claims to do this because he believes the Horde has changed - but Anduin himself is a pretty pisspoor judge of character, to the extent that Sylvanas repeatedly surprises and runs circles around him on the basis that she does things that Anduin doesn’t expect. Why should it be different with the rest of the Horde? When has Anduin been accurate for that matter with any member of the Horde save for Baine? Why further, should anyone believe that the council will be able to restrain the Horde’s ideology and impulses any better than Vol’jin or Thrall did?
Stormwind has repeatedly demonstrated that it is using the Alliance to its benefit, and that it’s either unable or unwilling to assist the Kaldorei. It won’t even act in respect to the risks that the Night Elves face. In either case, their membership in the Alliance is therefore something worth questioning.