In my opinion a wheel motor offers options in the design. in many cases a a central motor design can cause higher development cost in the driveline.

轮毂电机成本低，动能可回收；中置电机对整车行驶过程中的操作性，稳定性要更优一点。

There is a limit to torque on a given motor relative to its diameter. This is due to the maximum magnet strength that can be utilized. Motor torque is directly proportional to diameter times length times magnet strength. This is the reason rare earth magnets are used for most modern motors. But even with their higher magnetic forces, there is still an absolute limit for a given physical motor size.

With all that said, there is a significant limit to the torque and kW for a motor placed in the hub. And because it’s direct drive, there’s is no method to multiply the torque There isn’t a practical way to exceed the absolute limits of a hub mounted motor.

On the other hand a much smaller motor (physical size) can be run at a much higher RPM in a centralized location because gear (or chain) ratios may be incorporated. This can result significantly higher kW and torque available at the rear wheel. There is essentially no absolute limit to the kW output for a centrally mounted motor.

For simple bicycles and scooters that run at lower speeds and loading, the limitations of a hub mounted motor are insignificant. For larger motorcycles that run at higher speeds, a hub mounted motor may be incapable of providing the required torque and kW.

Cost wise for a given kW at the rear wheel, a central motor with some sort of gear reduction is probably less expensive. Because a much smaller motor may be utilized.

While a hub mounted motor can be simpler, it has some severe kW, torque and cost limitations that can’t be mitigated.

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I’ve worked with industrial motors of all types and especially servo motors which are quite similar in construction to the motors used on vehicles. In almost every case, a smaller motor coupled with some type of gear reduction has much higher capabilities and lower cost. A motor sized for the same application without a gear reduction will need to be much larger and have a higher overall cost.