there's a pressure on several fronts: to not be seen "pandering" to the male gaze, and also to be "authentically" female-centric. I wonder if that's why f/f is seen to be so conservative?

I think you've hit on something here.

Of the western terms, my favorite is definitely femslash; but if all of fandom spontaneously decided to start using yuri for everything, I wouldn't complain.