High elves had that already in MoP.
LOL. Who was Jaina’s lieautenant? Which group was the main fighting force for the Kirin Tor? Who was the character that actually quested at our side in the Isle of Thunder intro scenarios? Which character actually had a personal reason to hate the Horde?
Vereesa’s role in 5.2 is almost the same as Umbric’s in 8.0, except better, because she actually had personal reasons behind her actions.
And, unlike Umbric, Vereesa has had roles in multiple expansions.
Yes, you can. Any magic-oriented group could have replaced them.
Helping in Undercity? Lightforged troops could have beamed from the sky. Heck, the Silver Covenant could have opened the portals. Portals are not exclusive to void elves. Even Lor’themar’s “traitors” line could have been applied just as fine to the Silver Covenant.
Alleria facing Sylvanas in the throne room? Could have been Vereesa just fine. Alleria’s powers didn’t play any role in that encounter.
Void dinosaur? Dark Iron shamans could have summoned that same elemental they used to genocide goblins in Zuldazar one patch earlier.
Void elves are filling space. There’s no particular role for them, they are just there, having small cameos.
No other group but Silver Covenant would work as the faction that would side with Jaina to expel the Sunreavers.
No other character but Vereesa could have stated the murder of her husband as reason to not stop fighting the Sunreavers.
No other group but high elves would be better to answer Halduron’s call in Zul’aman.
Void elves are a plot device. All they have is flashy stuff. High elves have actual history in the setting.