Both Brose and Bosch have plants in China, you can search for it. I don't know which parts are coming from where and honestly I don't care, that is not the point.
What matters is QC not where the component is assembled. For a motor which was assembled in Germany, Brose motors had their fair share of belt issues in the past so just because you assemble something in Berlin doesn't mean that it is going to be reliable.
First of all I didn't say 1000W will generate less heat than 500W, that depends on the efficiency at which those outputs are generated.
Second the mainstream mid drives will dial back when put consistently under their peak power output for a prolonged amount of time, my Bosch cx does it.
But more importantly larger electric motors are simply more efficient due to having thicker coils, larger core size etc.. So given the same controller, Bafang ultra will be more efficient than a mainstream like Bosch, Brose etc. for the simple reason that it has a larger volume and contains more copper. Another important point is heat dissipation , more mass means better heat dissipation so an Ultra will tolerate heat better than the smaller counterparts.
Every motor have their own place, there is no point in trashing something just because you don't like it.