Dunno about Rih.
But Katy and Bey do indeed write lyrics and melodies to varying degrees based on the intent and purpose of the song.
Basically the same thing as Taylor.
I don't like Katy's voice at all. The only song I actually liked her voice in was her cover of "Hackensack" which is amazing. Her pop songs have a nice way of hiding it for me.
Kacey's voice is very boring and monotone but it's very pleasant and smooth.