I'm talking about the disc surface.
I can understand the confusion because this discussion has gone off on a bit of a tangent!
The OP was talking about the hub and caliper as far as I can understand.
I agree.
Suffice to say that the rust shown by the OP is a common phenomenon on most cars and that EV’s are more subject to this problem, due to the reduction in use of the foot brake, due to the addition of having Regen braking available.
It’s a unfortunate by product, I guess ?.
So it is, what it is.
All of our driving styles are completely different of course.
I am a Regen level 3 person myself, I guess you could always reduce your level of Regen and therefore give the friction brakes a bit more work to do, now and again ?.
This would help keep the brake surface of the brake discs a little bit cleaner, but to be honest I have become very use to using the higher level of Regen and therefore do not want to make this sacrifice.
I am not worried or concerned about the slight rust on the brake disc’s / rotors ( USA term ) on my car.
As said before, this rust is unavoidable to a large extent.