I never read these huge posts as im far too lazy. But ill make an exception here as I read the article yesterday and can probably afford to skim it. It was a very good article I agree.
You left out the super massive singularity at galactic core. Several billion suns of mass added to general very high density of stars at core [1/3 of a ly apart] means a very respectable grativic sink. Enough to keep galaxy together and rotating in virtually flat space of intergalactic realm. Its not about how much mass. It's about where it is and how concentrated. Reality is not homogeneous. It clumps. Singularities are in my opinion far more important than science thinking slates them to be. They are stellar evolution.