I don’t actually agree with most of your original post. It’s too dependent on a whole lot of what ifs and things that are not actually canon.
But in general, I will agree with this one quoted part in sentiment, because Sylvanas never should have been made Warchief ever at all. She had a record of breaking Horde laws, and had a record of being dishonorable. What’s more, Blizzard went out of its way to say that the Broken Shore situation was never clarified at all until after Legion in Before the Storm (and even that I’m just waiting on being retconned any way so that she had intentionally planned to leave Varian for dead all along). At least now we’re finding out Vol’jin was possessed by something that wanted her appointed for its own purposes instead.