I haven't done a hot take in a while but here goes: When it comes to villains and antagonistic characters in general - you don't always have to spare them or redeem them. Sometimes the fun of having a villain is them being villains and paying for it.
Gul'dan was a villain done right in so many ways. I like to think they liked him so much in Warlords of Draenor that they kept him around for Legion just to be imposing. The start of Legion will remain the best part of the expansion for me.