The title pretty much says it all.
Imagine if there wouldn't be no 8.3 - it wouldn't matter at all. Shadowlands basically starts directly after 8.2.5 and Sylvanas disappearance. All of the stuff in 8.3 doesn't matter for the upcoming expansion. It's just there to finish some plots they (unnecessarily) opened in BfA.
With a clear faction war storyline this expansion could have been good, ending with the disappearance of Sylvanas and then the Icecrown interlude to 9.0. There was no need of the Old God / Magna / Azerite stuff at all. Clearly it doesn't matter for the future as the focal point is Sylvanas and just that.
8.3 already turned into a non-event due to its announcement three weeks before Blizzcon and being completely overshadowed by Shadowlands (pun intended). It's so sad they waste the last Old God in a manner like this, with all the amazing Titan stuff, Wrathion, the Forge of Origination etc. - all stuff that basically seems to not matter at all for 9.0 and the events caused by Sylvanas. Yes, we cannot judge yet, but from what we know basically everything Old God related stuff from BfA is pretty much pointless for Shadowlands.
They could have easily spun an expansion around faction war, then Shadowlands and left N'Zoth and the Old God stuff for an expansion a la Black Empire. Yet they chose to throw away all of it in a fashion that it seem to be irrelevant for the future of Azeroth. This just makes me sad.
Both 6.2 and 7.3.5 more or less caused the upcoming expansion yet 8.3 has basically no effect on 9.0, 8.2.5 has. This isn't just weird from a storytelling perspective.
And when we take this further, not even the faction war mattered as it basically changed nothing - factions are there to stay, mechanically nothing changes. Horde gets a council, that's it. All this was just done to build up Sylvanas as a demigod anti-hero / villain or whatever. In the end all of the events in BfA didn't matter at all. Only Sylvanas did. Is this good writing?