Slapforhits, From experience, you may have seen the advantage of a great screwball or curveball at the collegiate level. you've played the game, and you know through firsthand experience. I guess it all depends on the pitcher throwing it, right?
Hillhouse may have a nasty combo of those three, so that's his opinion, plus, he's a dude. Jackie Traina throws a killer curveball and change combo. Same can be said about Dallas Escobedo's riseball. Erin Aravelo last season succeeded using her drop.
I think that one cannot generalize fastpitch softball to the level of three needed pitches. It comes down to finding what pitches you throw best and then making them dominant.
so, in short, I have answered my own rhetorical question. Unless you were thinking of something completely different...