Are you suggesting that if the Mavs acquire Deron Williams they will be bad enough to end up in the bottom 7, and that the Nets will improve?
D-Will is a ghost of what he once was -- he's now not a far cry from Jameer Nelson -- but I don't think he makes teams worse. Dallas would be anchored more toward the middle if they could get him without giving up very much. Still not very good, but not likely to fall into the bottom 7 unless he and Dirk are both injured for long stretches.