The point here is that at Legion launch and throughout every single Legion patch during the life cycle of the expanion your statement wasn't true.
Only after the Legion story concluded, we found out that Suramar, despite it's rich Night Elven history, is joining a controversial side of the conflict.
1. By your logic if orcs were added to Alliance at any point (they wont) it would make all expansions favor Alliance.
2. I will agree with you if devs keep the current underdevelopment of Allianve side of the story until the closing chapter of the expansion when something big happens in Alliance.