Deron Williams was bad in New Jersey with a bad cast
of teammates/coaches in my opinion. While he pushed to leave Utah, he was an elite PG their for years.
In Dallas he will have a proven no-nonsense coach. A team leader in Dirk that will have no problem putting him in his place and the extra motivation of playing for his hometown team. It may not work, but I am confident he will do better than Rondo did. Even if he plays as well as Jameer Nelson did last year they will be a very good team.
A 109 defensive rating is not good (a 90 offensive rating is horrible, but the guy is obviously not polished yet offensively) and the negative box score plus minus is also bad.