On MPE all channels would be one patch but the dynamics of that channel are sent per string. So if you do a string bend (again probably not with a hammond organ) why would you want all the strings to bend by the same amount - pitch bend is a per channel message, normally you would just want the bending to be done on the string that did it not all the strings.
Not having mpe reduces that flexibility and takes you back to why are you putting up with the downside (over a keyboard) of poor response when you are not using the upside of expression.
The GR pedals process the signal directly as well, but that is a cover on the tracking, not too surprising as the GR55 is 13 years old now, came out basically when the first iPad did, the speed of processing has changed a lot (although the speed of calculating a frequency from a wave not so much).
So it seems like the technology is the same, but a bit more modern and with the midi built in.