Like, realistically, I think most people could probably find their way into a relationship with a variety of other people under the right conditions and circumstances, but I'm likely not going to be interested in that enough to want to read about it!

Oh, yes, definitely!!!

I am sure she went on dates in college and had a perfectly fine time.

Absolutely.

But I've got no reason to read Youngshin/any of her colleagues or Youngshin/random college classmate because the show hasn't done any work to make that interesting to me

Very very true.

I actively would never read Youngshin/Moon-shik because it is important to me that that relationship is not actually romantic but is in fact the specific dynamic between an older cousin who got very parentified and the kid they used to babysit.

YES!!! Making that relationship romantic/sexual in any way would make it less interesting than it is (and also squick me some).

(I would however read Youngshin/Yeon-hee because their three episodes together were very compelling.)

I think I would read this too!