It is only a filler expansion if Azeroth is not united by the end of it. BfA has a lot going for it, and I very much doubt a lead developer would make an "azerite=uranium" comparison lighty. This pretty much confirms armistice under the threat of MAD via azerite WMDs as, if not at the very least a plot point, the end point for BfA.
Everything up until then? Fluff and filler meant to stoke faction pride until you realize United Azeroth was an inevitability as far back as MoP. Even fucking Wrathion knew and he's an annoying child that can't even twist politics, except for maybe whispering into Vol'jin as the loa and picking Slyvannas, thus sparking another faction war. But that's just a theory! A game theory!
(You can find evidence of Wrathion most definitely still succumbing to void/old god influence because without wards, not even the Hammer of Khazgoroth cleansed Ebonhorn could deny their influence. Wrathion is most definitely a corrupted black dragon and it makes a lot of sense for him to have manipulated Vol'jin into picking Sylvannas, knowing full well how that sits with the Alliance.)