I'll start at the bottom, the cranks, gears, chain, and bearings, will need much more frequent replacing due to several times the power input they are designed for. The install requires completely replacing cranks and bottom bracket, and the center of gravity issues do not really depend on the motor at all, battery placement is generally much more weight and is the same for all types. Only a few mid-drives have true torque-sensing, though this may be one of them. This can be added for hubs, though most find the standard PAS sufficient for much less money. The standard is simply RPM and not true Torque sensing. Also note that if part of your drivetrain breaks, you walk the rest of the way. Oh, yes, there is also additional offset to the cranks which for some people with knee issues has been a deal breaker.
Power thru the gears seems like such a good idea, most people however just do not need it, it is a gimmick and unnecessary complication. Most hub users will state that multiple gears really are no longer needed.
However, your situation is not common and your hills are extreme. The rule of thumb is you need to keep your speed from dropping below 50 percent maximum for a hub motor, though using partial throttle or PAS reduces the overheating problem. Long times at slow speeds with hi power demands will severely overheat most hub motors, though there are multiple cooling solutions available. The mid-drive thru the gears keeps the motor spinning at a high speed even when the bike is slow, and gets around much of this.
But, it does this thru reduction gearing which for many units has been somewhat problematic. Meaning a small plastic gear which breaks a lot, or a metal one which lasts but can be quite noisy. Obnoxiously so for some folks. Most hub motors are very quiet, and DD units are near totally silent.
Yes, it can be confusing and there is a lot to absorb. What I would recommend is to search out actual user reports, from people who have had their kit for significant periods of time, get their opinions and ask about their conditions. Be alert for salespeople and their hired shills, these are quite common on some sites and the mid-drive kits frequently have higher profit margins, some of the more aggressive vendors tend to specialize in such products.
I changed my mind several times before I bought my kit, there are many factors to consider and each type has its own pros and cons. What is best for your needs is something only you can answer, but you must define what those needs are, what is important to have, and which type of kit, and specific hardware, best meets those needs. There are questions you have not even thought of, yet.