heres what the stats say about how he plays when we win.

The most dramatic changes are FT%, assists and scoring, in that order.
Free Throw percentage in wins vs. loses is drastic, and I can see how this makes a difference for us because we lost so many games by 6 points or less that if he is making his freethrows, we have a better chance to win.
His jump in assists between wins and loses is significant. Teamates are scoring more off of his passes, which doesn't necassarily mean he is passing more; it could mean he is making better passes, or it could mean teamates are just hotter in those particular games, its hard to tell without watching those games.
He is scoring slightly less, not necassarily shooting less, but 2 points less is significant and it must be that way for a reason.
His defensive numbers are slightly better in wins: his steals, rebounds, and blocks are all slightly better. He needs to D up for us to win and we all already know this.