stormheim happens way after the heroes joined the classhalls, so she, as head of the faction should know about.
The factions did fight the Legion, in their places, but we know it was saurfang who lead in durotar/kalindor defenses, they sure didn't sit on their ass, but Sylvanas did next to nothing to hold her speech in vol'jin funeral.Also, while Blizzard doesn't feature them because that'd require giving the orcs screentime against their main nemesis we're told later on that the Horde was fighting the Legion throughout so we can assume they didn't sit on its ass for the extent of the conflict.
Yes, but in the RTs they didn't joined the horde, when they did, there should be a line to not be crossed by definition. Horde don't care about silverpine or other humans experiments because they don't know, its not their problem, the problem is when this dynamic is shifted, putting sylvanas and the forsaken on the spotlight would put those things on the light, and the imaginary line will be crossed, and thats why we had some of the interactions in BfA(like rokhan and Talanji regarding sylvanas actions) was a matter of wait for things to blow up, they just blow up in atomically.It's not a red flag in as much as it's how the state was founded as far back as the RTS. The Forsaken have a pretty transparent group-based morality. It's why nobody cares that Stillwater experimented on humans but the second they see that he's zombifying other Forsaken he's slated for permadeath. It's a transactional viewpoint. As regards Eyir, i've already made the case for why even if that weren't the case any leader who knows that her and her people's fate is to go to turbo hell would not only be justified but morally obligated to prevent it, especially if the means hinge on enslaving a third party.
Like i said, even if enslaving Eyr should be good for her and the forsaken, is a problem when affects the horde and/or put the horde in a bad light.
Sylvanas warchief was DOA, if she didn't step down from the position it was a matter of time before she going full villain, exactly to do what you said, escape turbo hell, and how she does this? exterminating her enemies, that in the end, will mean, exterminate the horde as well because their innate difference