I have made playlists with a handful of artists and songs with the specific purpose of using the "go to radio" feature to listen to more of their music and discover like artists - and NONE of the artists or songs on my playlist show up in the radio. That defeats the whole purpose. And for newer independent music, the suggested artists don't feel like they make much sense.
I've also seen other posts saying that Radio stations need more variety - I agree with this as well. Example - I create a station based off of a David Bowie playlist and I get very little Bowie, and then a bunch of Talking Heads and a handful of other artists repeated over and over. And Pavement shows up in like EVERY station I make, no matter how many times I "thumbs down" them!