I only own the 535 since 1 year and a half and replacing the tyres was in my first mods. So I don't know about the longevity of the Sport Demon that were on it.
Yes quite deep scalloping on the sides too.
I replaced the front tyre at the same time. Wear is very even. It will last a lot more time.
You know, I drive fast most of the time and only on small roads with a lot accelerations, braking and twisties. So maybe that's one of the reasons of the short life of the rear tyre