Sessions is better than Nate, and Parker is better than any SF on our bench.
Jamison is a better offensive player than BBD, and he's a better rebounder. He's not as good on defense, though, and he can't play center.
I think, on balance, this trade would make us better, even if it would leave us a little thing at center. That said, I don't think that Cleveland is getting much value here, so I think they'd pass. I can see them taking salary dumps for Jamison and Parker, but not for Sessions.