The first two things don't make sense huh?
So when he's on the court, opposing teams score 98 points per 100 possessions. When he's off the court, they score 105 points per 100 possessions.
Hmm yeah I'd say he's helping them win.
In terms of winning, it's not showing on the scoreboard.
According to 82games.com (meaning this might not be updated), The Bucks are outscored by 14.5 points per 100 possessions when Sanders is on the court. The offense scores an anemic 90.7 points per 100 possessions with him playing, and allows 105.2 points.
The defense is indeed better with him on the floor (allowing 109.4 points when he is sitting), but the offense greatly improves (100.7 points / 100 possessions when he is not on the floor).
What that adds up to is that the Bucks are 5.8 points per 100 possessions worse with Sanders on the floor.
Now, +/- and on-court / off-court aren't my favorite stats, especially without context. However, these numbers suggest that the Bucks aren't winning when Sanders is on the floor.