Nice definition but I think you (intentionally?) forgot to read/understand and highlight certain words ?
By the definition you provided:
"an
agreement or a settlement of a dispute that is reached by each side making concessions."
I think it's clear there is no agreement that void elves are an alternative to Alliance High Elves or there wouldn't still be requests.
The definition of "settlement" according to the cambridge dictionary is:
"an official agreement that finishes an argument"
and the definition of agreement given by the cambridge dictionary is
"the situation in which people have the same opinion, or in which they approve of or accept something"
I think it's clear based on forum posts here and on the official wow forums that Void Elves are accepted as a compromise to Alliance High Elves.
Therefore according to the definition you provided they are NOT a compromise.
Blizzard also never claimed Void Elves were a compromise (and they never would since their customers have no say in their development decisions and don't have to agree with them).
What Blizzard did clearly state was: "
...the Nightborne allow the Horde to play something that is similar to the Night Elf, and the Void Elves allow the Alliance to play something that's similar to a Blood Elf. So, that's kind of a, swapping of the factions where you get to experience the other factions."
-- source
The last sentence explains why they went with Void Elves rather than High Elves. Void Elves are in a very similar position as Blood Elves were in Warcraft 3/start of TBC. Blood Elves were effectively mana junkies fighting their addiction while Void Elves are mental patients fighting to retain their sanity. High Elves wouldn't offer this experience now that the Sunwell has been restored and they also don't share the mana tap history of the Blood and Void Elves.