NOTE: I've calculated the Team Winning Percentage for Gilbert Arenas by combining the record of the Washington Wizards and the Orlando Magic for the time he's played with either team.
One obvious thing that separates the Hawks from the Cavaliers, Wizards, and Kings is the presence of just one of their players on this list. Another is that Johnson (TO%: 8.8) turns the ball over far less often than any of the other players on this list. Jennings is next best in that regard, turning the ball over on 12% of the possessions he uses. This is really how Johnson is holding on to some semblance of offensive value while playing with a bum elbow. For example, Arenas (TO%: 17.2) has turned the ball over almost twice as often as Johnson so far this season.
Rounding out the offensive picture, three players on the list (Williams, Jennings, and Arenas) have a higher assist rate than Johnson this season. All but Williams and Arenas have a higher offensive rebound rate than Johnson.
If you were to lower the Usage Rate threshold to 18%, Trevor Ariza (46.8 TS%) would join Johnson as the only other player qualified for the FG% title with a TS% under 50 who plays for a team with a winning record.