Good post - some comprehensible synthesis.

Could one say, the closer the motor approximates the riders power, the better? Just as an example.

e.g. if a factory bike is set up for humans to pedal, then presumably a bolt on motor with similar power and torque &~rpm to a human, would seem a sweet spot, except, a rider is not very much power usually.

This pedal cadence remains a puzzle to me, and your comments help. Dunno, but the balance rarely seems right on my middrive. To get rpm right, is to get pedals wrong it seems.

"some are better engineered then others and with one that I couldn't adjust the gearing ratio easily myself I'd want to be pretty sure that those who engineered it took into account the finer points of matching the electric motor to the human motor where small changes can make huge differences in how efficient, how powerful, and how "good feeling" and smooth the electric motor works together with you.", seems to argue for a factory bike vs a bolt on kit?