it ultimately played a huge role in derailing the series plot
The problem is two-fold: on one side as TheHarbinger said there was a clear need to make every story "standalone" for new players to get in, making the plot development haphazard at best. The second problem is that ME2 was probably the apex of the companion-based writing that Bioware fell after their success in BG1. See, people
truly liked companions in BG1 and BG2 even more, and thus companions (and romances) became an even bigger and bigger part of the games, with obvious consequences. But people were happy with it because you got the pseudo-romance angle. Reading them now they're
embarrassing at best, Bioware romance dialogue was worse than even the worst Japs or George Lucas could throw at you, but even in the 2000ies you didn't get high-budget games with those themes.
Mass Effect 2 is essentially a game built
around companions, companion banter, and companion romance. 90% of the game is recruitment missions and loyalty missions, the entire ridiculous setup is to give you more time to banter around with the companions because people truly wanted the pseudo-social experience instead of a coherent plot. If you
don't indulge the game you get a "bad ending" because you didn't engage with the companions.
I'm still stuck at the beginning of ME3 in my replay, every time I try to fire it I'm struck by the "SUDDENLY REAPERS ARE IN THIS VERY ROOM WITH US" that makes everything you have done in 1-2-DLCs feel meaningless. What have you done exactly if in
five minutes the squids come barreling down to Earth and kill everyone?
Hell, even
Halo, the apex of 2000ies sci-fi shooters, despite retcons and middling Halo3 writing, has a better buildup and arguably
better writing. I can remember Gravemind's quotes and Sergeant Johnson's chatter, but what do I remember about ME? In ME1, Sovereign's reveal, because it was foreboding (and then
completely retconned)? In 2, Mordin singing?