It's like saying that Arthas in WC3 wasn't the Lich King or that Illidan was a Demon Hunter before becoming a full Demon. Also the players have toned down versions for lore and gameplay reasons, not less powers overall.
I could see a Dark Ranger doing a "cloud of death" like the BfA cinematic for AoE damage, but not a super strong one that one-shot everything. I could potentially see them reanimating but not armies like the DK doesn't.
It is all a matter of scale.