I would like to point out something that I think might be getting ignored here or maybe I'm just full of rubbish. Either way, here is my point:
Do you think it's possible that what you see as an "obsession" with MP on BioWare's part is actually just a difference in timeline for how content can be provided based on what it is? What I mean by this is that it takes a longer amount of time for the SP team to develop SP DLC than it does for the MP live team to throw a switch for a weekend challenge which, really, just amounts to playing the game but just doing a particular thing, such as using a certain weapon or character. A weekend challenge is not really "new content", it's just something easy to do to keep the MP fans engaged while the MP team spends time working on actual DLC content (which seems to take about as long as producing SP content takes).
That's... not really something you can do with SP content. Such as a splash screen saying - "SP Weekend Challenge - complete five War Table operations!" You know? So, naturally, seeing a splash screen every weekend alerting MP players to a new weekend challenge is naturally going to make things look like there is a greater MP focus.
But in reality, I feel SP actually got more overall content or, at least, they were fairly even for DAI. You listed things such as DLCs, new maps, weekend challenges as showing a bias towards more MP content. In reality, SP and MP got the same basic amount of DLCs. SP got Black Emporium (small/minor), Jaws of Hakkon (sizable), The Descent (sizable), and Trespasser (sizable). MP got Destruction... which just added three "alternate" versions of the original three maps and threw wild animals into the mix as enemies. I'd call it a very small DLC, on par with Black Emporium size, and also introduced an awesome game-breaking bug that went unfixed for several months because BioWare released it right before they went dark for the holidays. Then, MP got DragonSlayer DLC, which was sizable - it added a new map, an optional dragon fight on the new map, and some new character kits to play. And that was it. That was literally all of the MP DLC. Two, compared to SP's three. We did get two more playable kits trickled out to us and two new (super annoying) enemy factions around the time of Trespasser. So, I suppose if you add those together with the two official MP DLCs, you could maybe say SP and MP were fairly even as far as new content goes.
However, I do speak as someone who likes both modes, so obviously I have a bias to not hate anything related to MP simply on the account that it is MP. I really did enjoy ME3 SP and loved ME3 MP. I really loved DAI SP and sorta enjoyed DAI MP. I don't feel either of them took away from each other. I understand that you, among others, feel very differently about that. I'm sorry, but I am not sorry for enjoying both the SP and the MP of the last two games.