Which cutscenes are you talking about?
Also, I should add that I think part of the mixed messaging was due to poor internal communication. We know from Christie Golden that the Warbringers shorts were well underway when she joined the staff in May 2017, but the devs were claiming in April 2018 that they wanted “to end up in a place where the Horde can make an argument that the Alliance started it and vice versa” (Travis Day, Invenglobal*).
I don’t think it was ever going to be “both sides” after Afrasiabi decided to trash Sylvanas just to spite Danuser or whoever.
I agree with you on that one. It’s clear from pre-expansion publicity that the war was originally supposed to go much further and probably was meant to take up the entire expansion. I would not be at all surprised if they cannibalized the entire next expansion for the Old God plot.
*See this thread: