Woosh, you are better than that. My arguement about efficiency is that motors have a natural speed range over which their efficiency is high and it drops off when rotating much slower or higher... with a mid drive that is possible. With hub drive it is not.
The internal design of a motor and its controller takes into account the correct RPM range for the job in hand. In that respect there will be no difference between either motor, hub or mid, "horses for courses!" so to say.
Furthermore, modern BLDC motors are very efficient, up to 90%! See here:-
en.wikipedia.org
BLDC motors are typically 85–90% efficient or more. Efficiency for a BLDC motor of up to 96.5% have been reported, whereas DC motors with brush gear are typically 75–80% efficient.
This is partly the reason that many items are now being built with an electric drive, soon very large ships will be also be so built!
Secondly the other point is what happens when the cyclist is peddling faster than the motors speed. In a mid drive a very light clutch disengages the motor and gear assembly. Where is the clutch on on hub drive? .. even if present the planetary gears are rotating and this is pure drag. .. especially when there is no power assistance.
I know that some bike hub motors are built with gears and clutches, insofar people here have mentioned that, and I do believe both mine were direct drive motors, but they would "free wheel", with no noticeable resistance.
Apparently, some have no freewheel, and without battery power available, are heavier to ride (I have been told!). But such a blanket statement about hub motors as you made, is not fully true.
I also believe that some (cheap) hub motors , are possibly made with no gears, direct drive to the axle/wheel, but SEEM TO possibly have a free wheel, probably the cheaper ones at a guess. But I do not know that as a fact.
Similar to the ones I just happened to have bought, as hub motors with gears, generally make noise, not loud (when working correctly!) of PLASTIC gears meshing. But neither of mine have done that, even though the first one did a really very high mileage, before I gave it away in a fully working condition.
But as I never have needed to dismantle either motor, they just simply worked, I cannot say that for certain!
I also feel that the hub motors are generally better cooled, which I am sure further aids a long, trouble free life!
You may find this video informative about both hub types:-
Also the following website basically says what many here have already said that good hub motors versus Mid motors, as hubs require next to no maintenance and last a good many years, as well as being much cheaper than mid drives:-
Electric bicycles are becoming increasingly popular forms of two-wheeled electric transportation for both commuting and pleasure riding. The two most...
electrek.co
He seems to cover everything correctly as I know it.
But me having heard about the problems that some Bosch owners have had over the years with their expensive "steeds", motor problems, gear problems, service problems and also guarantee problems, has kept me and my pocket book FAR away from such possible problems = No Mid Drive Bikes!
But each to his own choice of motor style, and thats the way it should be.
regards
Andy