Partly. Without Webber, Divac and Christie setting screens and throwing him sweet passes he just couldn't play his role as he had. Also he didn't want to be here and it showed. It's much harder to do your job if you don't like where you're working.
But Artest brought everything this team needed (defense, low post presence, confidence, edge, etc.) plus the young guys Martin and Garcia developed.
Combined with Bonzi coming back, all these things have led to the turn around.