The Burning Legion was a threat to Azeroth since the war of the ancients and they attempted to invade Azeroth several times.
No one (in lore) ever considered invading Argus, why now? What has changed? Where were the preparations? Wouldn’t you want to prepare yourself or at least have a plan other than yeah let’s just do it because why not lol burning legion lol?
Where does that Naaru spaceship come from? is it a new one or is it the Exodar? What would replace the Exodar as a capital city?
And by all seriousness. Did you read the last few books for expansion intros? They were primarily talks, emotions etc. Not much action going on, not much to portray in a cinematic or ingame.