Trading Theis for Wagner was a classic sell high buy low maneuver. Obviously, it could have been even better if Wagner had another year on his contract.
Theis has outplayed all expectations, and arguably, he has exceeded his abilities in his performance on the court. I love Theis and have appreciated his work ethic, intelligence, and humility on the court. But Ainge saw what happened in the playoffs last year to him. The winning formula is with a little more toughness and athleticism on the inside with Thompson and Williams.
He essentially traded Theis for a much higher upside player in Wagner. I don't think Wagner is a future all-star, but I can see a little Brad Miller to his game. If you watch his college highlights and compare how he looks to right now, it is obvious the guy has worked a ton on his body. It shows on the court. He demonstrated even last night the agility to drive by his man, and then counter with a spin.
The problem since Wagner came into the league is that he's never been able to put it together in on-court effectiveness, but the raw tools are there to be an effective rotation player on a playoff team. So far in the NBA he has played for a terrible Lakers team, a terrible Wizards team, and a terrible Bulls team. He hasn't played for a decent coach. He hasn't played with this much roster talent.
Ainge can make a hard sell to Wagner in the coming months to resign with us on a several year deal and develop his abilities under one of the best player-development coaches in the NBA. Ainge can say, "Look how we developed Olynyk, Williams, and Theis. Look how we got the most out of bigs like Zeller, Horford, Baynes, Johnson, Sullinger, and Theis. Signing with the Celtics is an investment in your future in the league. We can help you earn your staying power in the NBA while playing for a contending organization."
Unless another team with a ton of cap space believes in Wagner, offers him a starting position, and gives him a guaranteed huge contract (highly unlikely), I think any Cs offer would be the best offer on the table.