sorry for quoting myself, but I wanted to add something to this:
there are no perfect transitions and projections from team to team; and I'm certainly not saying DDR is on par with Bridges/Brown/Siakam, but when you gauge impact you can, to a degree, use winshares, Last season's marks for winshares (and since it's a cumulative stat I'll include total minutes)
winshares:
Derozan - 8.5 (2682 minutes) ---> .153 winshares/48
Siakam - 7.8 (2652) ---> .141 winshares/48
Bridges - 7.5 (2963) ---> .121 winshares/48
Brown - 5.0 (2405) ---> .100 winshares/48
BPM is a lot more rotation dependent, and a bit more team dependent, like winshares
BPM:
Siakam 3.1
DeRozan 2.0
Bridges 1.7
Brown 1.3
Siakam does get rebounds and assists at a good level, and plays ok defense. He gets a box score bump because of his overall versatility. Bridges is probably not getting enough statistical credit for defense, but he is a poor rebounder and to this point hasn't demonstrated consistent play-making.
I think some are undervaluing DDR's impact. And the more I looks at things, the more I question if Brown is really worth the 3rd pick and a 57M/year contract