like many others, the story of SL is just bad and the new lore we've gotten is uninteresting, and just badly written stuff you've seen in other fiction.
but for me, the issue was how Blizzard ended legion, then Danuser rushing through so much established lore in BFA so he could get to this fanfic SL garbage and his waifu's story :/
legion should have ended with a more complete version of us pushing back the legion and defeating KJ. Velen and the draenei should have gotten a more personal and involved ending with KJ. The expansion should have ended with us completely pushing back the legion out of Azeroth in a significant/final way, then Illidan revealing his crystal portal thing at the end to set up the next expansion
the next expansion then could have been us using that crystal to be the ones to invade the weakened legion, us being on the offensive for the first time. We could have use the crystal to go to legion controlled planets and save surviving army of the light members. This would have let the army of the light be more than 1 fcking ship with some draenei in it. And, each planet being a zone would have dealt with the "too much green" fatigue of legion, as the art team could be as creative as they want with those zones
then things like the titan revival, alleria/turalyon, sargeras and so on could all be used over an expansion, instead of rushed in one patch/raid. Argus could have been a much better series of zones, with more to it than what we got. Sargeras in particular, could have been more involved than suddenly appearing at the end of the raid and done with in a cinematic. The titans and their revival could have been a great expansion wide story, reviving each titan one by one with their own quests and story
alleria's story with the void could have been properly expanded on, instead of a few quests. Turalyon and his past in the army of the light could have been explored. Xe'ra could have been a more expansion antagonist slowly going more and more fanatical instead of how wasted she was. Illidan could have done more... and so on
now this is just me spitballing ideas, but the point is that there was SO MUCH lore and content that blizzard rushed through in 9.3 alone.
And the same exact issue with BFA: Azshara and Nzoth both wasted in one patch each, when both are easily expansion wide villains and places like Naz/Nyalotha had so much potential.
and by expanding on all these ideas, blizzard could have kept the story and next few expansions based in Azeroth... and not this stupid fanfic cosmic shit that Danuser is obsessed with :/