Keep in mind however that the only Void Elves who were transformed (as far as we yet know) are the ones with Umbric that got caught in Durzaan’s ritual trap during the unlock scenario.
How new Void Elves are gaining their powers has not yet been detailed by Blizzard in game or out. It’s logical to assume that new Void Elves are gaining their mastery of the void through a process similar to Alleria’s considering she and Locus Walker (her teacher) are right there to do the training.
And while Alleria did absorb great amounts of void energy from Nhal’athoth and L’ura, all Locus Walker says during the quests on Argus is that:
After some consideration, I have decided to allow Alleria another opportunity to pursue her destiny.
I suppose you want to know what that means, mortal.
Meet us deep in the Shadowguard camp ahead- my brethren are preparing a summons that will provide adequate energy for Windrunner to begin again.
Witness what happens when you harness the Void’s power.
This implies that only “adequate energy” is required to follow Alleria’s path, not specific types of void entities. “Adequate energy” could likely come from a variety of sources, with Nhal’athoth and L’ura just being conveniently accessible.
Telogrus itself is steeped in Void Energy as indicated by the Void Elf unlock scenario text, and the void storms that still linger in the zone after Void Elves are unlocked. This seems to indicate that it may be an ideal place to harvest void energy, whether from the void storms themselves or by summoning powerful void creatures to draw “adequate energy” from. There’s nothing in the lore or the game text that indicates that a Dark Naaru, or any specific type of void-infused entity, is required to harness the void as Alleria did.
And since players are typically never as powerful as their racial leaders, and can’t do many of the things their racial leader can do, it’s kind of unfair to expect that they follow the exact same path to their own power as their racial leader did, or at least they are at a point in their process that is further behind their racial leader.
Consider Alleria a master and player Void Elves as novices. It wouldn’t be logical to expect the novices to have consumed a Dark Naaru before beginning their career with the void. Alleria certainly had void powers long before her Argus story arc.