My expertise ended at pre-WoD when I quit, so I missed the 80000 retcons done to the Legion during it and Legion itself. So I guess former expert would be correct, but that's the same word games they pull on their own "experts".

But KJ generally seems to not be a betrayer in the direct sense. He offers power to those who are desperate (Illidan) or broken (Gul'Dan, Kael'thas) who accept and join him and he is surprisingly forgiving relative to most Demons as shown by Illidan getting numerous chances.

His actions are certainly corrupting, in pursuit of goals he doesn't tell them, and done through underhanded means. But he always seems to be willing to "save" them, usually by turning them into Demons and welcoming them to his armies.

The only major betrayal was joining Sargeras in the first place, but if you asked him he would consider Velen the betrayer there and his actions the correct one.