This whole situation is baffling.
The achievement: “I’ll Hold These For You Until You Get Out” was not meant to make the Warglaives exclusive.
It made the Warglaives an exclusion to the rule of Legendary Weapons i.e. disallow for transmog use. A rule which is being removed, in the same patch!
If making the Warglaives available to it’s original wielders cheapens the achievement (It doesn’t) make it a Feat of Strength, maybe make it so you have to finish the achievement to transmog them on other classes, or better yet replace the Warglaives of Azzinoth with a new reward useable only by Demon Hunters.