Radio is on by default, but turning it off should be one click on the queue. You’ll need to do that once per zone, but Radio shouldn’t start automatically after that.
You can also disable the Start Radio buttons from Settings > Play Options .
Also, we’d love to hear what you didn’t like about Radio’s picks 
https://community.roonlabs.com/t/roon-1-4-radio-feedback/35686/16?u=mike