Also, to add to that, your BMW mechanic ripping you off charging twice the money's for same work.Braking distance with rear brake is three times longer than with front brake. So, the more you use rear brake the earlier you have to brake.
If you can use rear brake, without braking earlier, it just indicates that your current front brake usage is very inefficient. And that is one reason why your lap times are slow.
All in all quit biking.