I don’t believe for a nanosecond that Garithos would of honored that deal if he even got a whiff of the fact that the Forsaken wanted any part of Lordaeron. Maybe they could touch that up in reforged now that they have less narrative limitation to work with, who knows.
And like I get that their first action being one of aggression towards the living would put a damper on trust, but it isn’t a thing that comes up that much. The only people who knew about it were folks like Kristoff who were d***s for their own reasons, and so for all intents and purposes their dealings with the greater alliance were a clean slate.
I would argue that after dealing with the worse aspects of humanity they sent a delegation to people they thought were better, got rejected, and THATS what they are complaining about.