You're trying so hard to save face its painful. As if casting holy spells as an undead.
#1: fel magics do not mutate draenei any differently than any other race being corrupted by fel magics. Literally every race is subject to this, draenei are not special.
https://twitter.com/Loreology/status/489778343903244289
#2: Not all draenei are light worshipers or arcane wielders.
#3: Their affinity for arcane is the very thing that draws the legion to them, why would they want to continue to practice arcane magic knowing it could draw the legion to them?
#4: Orc shamans were draenei's mortal enemy of draenor before the legion returned, even after suffering the genocide and being mutated by the red cloud into broken the draenei were able to look past not only the fact that it was their enemies magic but also that a broken who they shunned and cast out would be the one to teach them shamanism after that broken (nobundo) adopted shamanism having lost his ability to wield the light.
You seriously have no idea what the hell you're talking about here.