When talking about ts, we need to keep in mind AA is also running in the background with it. When calculating damage output of ts vs cssa, you need to put in ts + AA then compare it against csaa (since csaa replaces AA.)
So in that sense, since ts does not replace AA, it allows us to benefit from skyfury beyond just the mastery, while CSAA does not and only benefits from the mastery portion.
Just remember taking ts means base AA remains, it’s AA that benefits from skyfury, not ts itself, well except the mastery part of it.