Ooof. I had no idea about half of this stuff. I've always wanted to play Divinity II but my first Divinity game was Dragon Commander which I assumed was just a side story. From what I've read, the pre-Dragon Commander games all revolve around demons and Damian and are somewhat connected. Then DOS1 comes out and the story revolves around Astarte and void stuff. Now, what do Astarte and the Dragon have to do with the Godking and the Seven of DOS2 I have no idea.
Coming into this game I knew there was going to be canon and continuity issues simply because it's a DnD game. In general, WotC doesn't respect the story of the video games even if Torment, HotU, and MotB are way better better than anything they ever came up with. I mean having Myrkul return after what happened in MotB is just lame. Though when it comes to this game everything seems disconnected from one act to the other, plot holes and inconsistencies in the main story and characters suddenly acting differently at certain points in the game.
I wasn't on the doomer side when it came to this game since Larian has listened to feedback when it came to gameplay (reaction system, push..etc) but this disjointed writing is pretty much a staple of Larian and should always be expected?
Myrkul coming back is more or less retconnable (the entirety of 5e is WotC pretending 4e never happened and just rebooting the setting like it was before the Spellplague, including resurrecting gods - if Mystra could be restored after what Shar did to her, then perhaps Myrkul could too? It's still a very cheap approach to world-building and one of the big reasons I don't care much for FR since 4e and afterwards).
As for the writing - more or less, yeah. Pre-D:OS days at least had an excuse of them having to barely finish the game running on the last good will of the publisher every time or heavily overestimating their capabilities (Divinity II's world map fits in a pocket of what was originally planned for the game - it's still an amazing game, mind you, with the expansion being especially neat). Beyond Divinity was written by Rhianna Pratchett of all people, and it seems like both that and Overlord are the only two good plots ever written by her. Now, though, their development still remains a poorly thought out melting pot it seems, and BG3 is a culmination of that AND greatly expanding their writing team in size but not in coordination and standard.