I have a yamaha (and older model) which I love, because it is 'just' a piano (to be fair it does have the options of another couple of voices but I never use them) and sometimes it is good to play just a piano and focus on what you are playing rather than the sound (the sound is fine but, its just a piano).
Above it I have a synth in case I want to play synth stuff, worry about sounds and control issues.
The piano is midi'd up, as sometimes I use it to record midi from, but I wouldn't actually really use it as a master keyboard for anything, I would use the roland with its synth keys and controls.
Or if I wanted real control I have the roli or linstrument.
Point is, for me, a piano is a piano and a synth / controller is a synth controller, and although I would run a piano sound from the synth, I wouldn't really run a synth from the piano