Originally Posted by
Thage
In fairness, this really only exists as a problem for TBC. Classic WoW's story was all about your character's rise to power and much more localized threats, mostly taking place in the Eastern Kingdoms, but with three notable global-scale threats (Ragnaros, Ahn'Quiraj, and Naxxramas) that establish your character as a new hero fit to walk in the shoes of those who came before. TBC is when multiple popular characters from the RTSes were heavily promoted and shown off as raid bosses, and the narrative forced to fit that--it helps that none of Illidan's commanders nor Illidan himself were particularly good people, with Kael being the most moral of the bunch and even he caps out at unscrupulous survivor.
They learned their lesson, though, at least for a while... then along comes Legion and the hamfisted whitewashing of Illidan because they wanted to present the Light as 'just as bad' as the Void after decades of the Light being generally-benevolent; I assume this sudden plot twist happened because the devs noticed how popular dark fantasy settings were becoming at the time (before burnout kicked in) and they wanted to twist and bend WoW to fit when WoW was always high fantasy with dark elements beforehand.