What are some events, issues and characters' returns or resolutions to a character, race or nation that took far longer and slower to be done or resolved than they should have been ?
When looking back at all the circus with Jaina returning to Dalaran, due to a prophecy of her being the future of the Kirin Tor, before leaving in Legion and then finally returning to her home in Kul Tiras and resolving her trauma and anger issues during BFA I do think that it would have been better for her to return to Kul Tiras and bring it back into the Alliance during MOP instead of waiting three more expansions of unnecessary and often chapeau dramatique for it to happen (I would also have entirely cut the Derek Proudmoore stuff that should have never been imagined in the first place).
There's also the very late resolution of the Defias Brotherhood storyline during Dragonflight, with Stormwind finally restoring its authority in Westfall and ending the Defias annoyance for good. It should have been several expansions sooner.
I have also already expressed my thoughs on the Stromgarde restoration, return of Danath Trollbane, and battle for Stromgarde happening during Cataclysm or MOP era with different actors (Forsaken, and as the main Horde force, and Gnomes instead of Darkspear Trolls and Lightforged Draenei) in my Battle of Stromgarde thread.