-mid drive motors will wear your chains faster;
-mid drive have to be serviced - money to be spent, time spent and technical knowledge are required; are you prepared to DIY or do you know a really good mechanic? even when you do not DIY and you spend money for other people's services... you still have to spend time because they won't come to your home etc.

-DD hubs do not wear your chains at all;
-you only need to replace bearings and should be careful to keep them in dry air as to not allow humidity go into the hubs - every cycle of changing temperature night/day will make the hub absorb new air when temperature drops and if air humidity is high the water will be absorbed by grease until the grease will be saturated with water. the only grease i know that literature explicitly describes as being truly resistant to water is polyurea grease.

if you happen to often expose the bike to the elements, leaving it outside etc., cleaning and fresh lubing your chains often and don't mind servicing more often every components that are vulnerable to corrosion then a mid drive won't have a too much impact for you in terms of spending time and money servicing it.

most DD motor hubs with no reduction gears weigh 6-7kgs and should have polyurea grease in the bearings;
some DD motors have reduction gears and weigh less, ~3kgs; those reduction gears have strong components that resist wear except the oil is contaminated or is not replaced after running in - if that has not happened at the factory.

-google "double planetary gears"
-google "Plastic Nylon Gear For Bafang BBS01" - an example of a constant fast wearing component made of plastic for sake of being more silent, more tolerant to the elements and neglecting in servicing the motor, less weight. if they made it to be made of metal there would be more vibration, more weight, the contaminated oil would be pitting it and would be felt in vibration and noise and therefore the consumer would complain in very short time. but nylon gears wear at a constant fast pace compared to metal gears that could be more resistant if proper oil replacement would be insured and the bike would not be left open to moisture etc.

they sell you stuff in order to cash in your money; salesmen are not engineers and don't really care about your ignorance but rather exploit it. you won't receive technical knowledge before buying nor immediately after that. if chances are you will wake up to your wrong decision 1-2 years later then they can't be blamed for it and then you either have to find someone else to use the system - that fits the profile - or deal with the unfit (to your needs) profile of the system regarding servicing it.

so, if you have lotsa money and you use your bike for kicks and fun then a mid drive would be better. the only exception is a high torque DD hub with (no clutch) reduction gears. a mid drive motor can even break your chain if you use the first chainring with a high-ish cog in the group set that means a high deflection in chain use. unless you are careful to completely avoid rust and change gears to avoid high deflections you are vulnerable to chains being broken. but that would not be the primary reason to avoid mid drive systems.

but... more weight at the end of the bike - more of a motorcycles and less of a bike. additional weight at the bottom bracket is not too much felt in turns. DD hub motors with reduction gears could be ok for that matter, less weight.

if you want a high power bike and you want to fast cruise with no heavy traffic then you should look at 6-7kg motor hubs. reduction geared DD hubs have much less power than the big motor hubs.