I'll stick my neck out on this!
True they are all different. However, I would suggest that “pianist” and “keyboardist” are terms that are rapidly converging. For example the large authoritative instructional tome “The Contemporary Keyboardist” by Novello is for anyone who operates a key-like device. The cover of the book even overlays the graphic of a piano and a keyboard. The word “keyboardist” is used to include the pianist.
What skills are you suggesting are unique to operating an electronic keyboard? Are you are talking sound patch design … then yes, that is a significantly different skill to master. Don’t take this wrong … but operating the pitch wheel? Or, are you talking the ability to realistically play the drums on the keyboard? Or playing an acoustic guitar patch on a keyboard and actually sound like a strumming guitarist (different technique required)? These are amazing skills that some have mastered, but I can’t say I’ve seen these skills demonstrated at a gospel concert.