1) It's very hard to define what the "mean" is with a group of players that have never played together.
It's not particularly hard to conclude that at this point this group is probably playing above its average level of defense. How much higher is tough to say, obviously, but some level of dropoff is almost inevitable.
Do we really think Smart is going to shoot 27% all year?
No, I'm afraid he's actually going to go lower than that, based on his shot selection.
Rozier is going to shoot 35%?
Looking at his career so far, yes, it's fully realistic that this is where he might end up, give or take. In terms of play style, he's Smart redux with a less horrible three-pointer and minus the premium defense. That's why they are such a particularly horrible pairing in the back court.