Good question, the Multi indeed doesn't have an effective back brake. I got used to it and saw it as part of the bikes character
Just drive it fast and full brake at the last possible moment with the front. Think that's how it's meant with the Duc. And then launch yourself out of the corner.
Brakes on the KTM are very nice and effective and they provide a good feeling. I also like the combined set up of the frond and back break, good emphasis on the front with a just little help of the back.
For me the original screen on the R is very good, no buffeting. I'm not considering the higher screen