I’m not sure what the ethical case against this specific route/mountain would be. Clearly there is the well publicised removal of one access track from the other side, but I don’t see cycling on the replacement as particularly contentious. Heading in from Tomintoul or Corgarff Castle, I’ve always thought of Ben Avon as the more “sensitive” hill. As you apparently have your wits about you and are happy to walk rather than skid down easily/already eroded steep bits (down to the sneck, for example), I would say take care and crack on.
PS – did you report back on your Macdui trip from the other week?
PPS – just seen your edited post – I’m not clear if you mean the problem being “riding” to and back from the North top from Avon, rather than the usual south approach, or descending a mysterious alternative to these?