yes, lower rpm means higher torque, in simple words
but in a small wheel you dont need so much torque because the advance of the small 16" rim give you a lot more hillclimbing ability as an high torque motor in a 28"rim
Important is what you want on speed and noise,
speed and torque you receive from a Bafang SWXU-Motor for 16" with 275rpm but the motor is more noisy.
Low noise but lower assist you receive from a tongxin nano or cute , you must decide what is your main point
Weigth is on small motor around all the same, between 1,7kg to 2kg
but tongxin and cute you can buy with only 85mm wide and Bafang is always 100mm wide
regards
frank