I don't think Mass Effect writing is bad, but I do think people are way off base suggesting Andromeda's writing is substantially worse than the OT. I also don't think Drew K is a very good writer, and demonstrably a terrible character writer. His books back this up as he has no clue how to do dialogue or characterization. That's something that at least Mac has over him. Mac doesn't know how to do overarching plotlines well of course.
I also don't know how you can say with a straight face that the OT had consistently "subtle" writing, especially when you are apparently comparing it to things like Jaal's loyalty missions. Yes, there were some ME2 loyalty quests with nuance like Tali, Legion, or Garrus, but then you had Zaeed, Samara, Miranda, etc. Let's not forget decisions like what to do with the Collector Base. In general it seems you are willing to buy into the often ridiculous nature of the OT's tales while cutting no slack for Andromeda.
I was of this opinion until I played more of the game, and I still agree that the original trilogy has a lot of dodgy writing in it (I'd actually throw Garrus' loyalty quest in there, too - why does he need you to permit him to shoot some dude with a sniper rifle?), but ME:A's problem is less its off-key writing moments, which are abundant, than its lack of good moments. It just doesn't hit the same highs as the original games, ever.
Basically, in my opinion, the writing in the original trilogy runs from, say, a 3 to an 8 on some stupid, arbitrary 10 point scale; ME:A runs from around 2 to 5. I consider it worse in that sense.
Edit - also, I think it's worth noting that ME:A's well-documented problems with animation in dialogue sequences probably damage a lot of players' perception of the writing. I find it borderline unplayable without subtitles, for instance, which direct my eyes to the bottom of the screen rather than to characters' faces. But in games with better animation (The Witcher 3, or even earlier Mass Effect titles) I play with subtitles off, which a fair bit more immersive.