EX and RS has the same 14' rim, same tire size to be clear, they are listed as 19 and 20 due to the different tire:
RS like MSP use the cst 1488 "18x3.0 street tire" who result precisely in a 19.5 overall diameter
EX use a kenda k304 who probably is a bit bigger, like the knobby for example cst 186 and kenda k262 are both 20.3 inch
MSP use a classic motor with central axle 2500W c38 torque version, 2000W c30 speed version
RS will use new generation hollow motor but basically the same size of MSP, we'll have a c38 torque motor (2600W) and a c30 speed motor (not sure 2600W )
MSP-RS lift speed are the same (80 and 98 km/h), and so the performance
EX and M24pro use new generation hollow motor with bracket mounting, the same on both wheels 3500W
to answer your questions: Why would they not use the same motors for the same size of wheels (EX and RS)?
becouse you don't have enought battery to use it, that's also why EX lift speed is 86km/h (2700wh battery) and M24pro is 106km/h (3600wh battery )
Are there three new Gotway motors (RS torque, RS speed, EX/MonsterPro)?
yes like i said at the beginning