The short answer is "no".

However, from your original post, you started talking about higher-end eBikes like Scott, Orbea, BMC and Cervelo, which are "bike shop brands". Then, you finished by saying you're looking at a couple of cheapies: MAHLE and Fazua.

In my experience, even the cheap eBikes rarely have motor problems, and I've had eBikes ranging from $400 (Amazon junker) to over $4k. (Yamaha Wabash RT) Motors are the LAST thing you need to worry about.

What you WILL find is that the cheaper eBikes have less refined firmware that runs the motor controllers. They just don't spend the time to get it all working really nicely together. My Yamaha, Bosch, Aventon and Lectrics were all pretty well sorted.

My Ride1UP had excellent hardware, but user-hostile controller programming. However, it was fixable with a few emails to Ride1UP.

Bosch, Yamaha, Lectric and Aventon firmware of the day were locked down pretty tightly as to what was allowed, but when used within the programmed parameters, it was very easy to use and predictable.

The $400 Sailnovo junker had smooth acceleration, but was not implemented in a smart way. The bike was a single speed, geared for about 9 mph, but the motor worked up to 20 mph, so that I was ghost pedaling from 11-20 mph.

The $1400 heybike Ranger (also sold through Amazon) had a ton of user programming options, all limited within legal parameters. That bike just had junky brakes that could not be made to stop screeching.

The bottom line is to spend a bit more for a more refined bike; it won't be the motor that disappoints unless you buy the totally wrong thing. (for example, a single speed for hill climbing)