Ainge said he made the deal because he thought it made the Celtics better. I'm not going to argue with him. He's the teacher. We'll see.
If you look at the deal, the only player they might miss is IT. But they only have a year of him left, and he didn't figure to score 28ppg again with Hayward around. Besides, Irving has a great contract which is affordable. Money is more of a factor for GMs than it is with fans. I also figure Danny was more willing to throw in that Nets pick than trade Tatum. He also has that other lottery pick to cash in on at some point.
A lot of this will depend on how Stevens is able to fit Irving into his scheme, and get the most out of him. That's true of the other newcomers, too. A real challenge for Stevens.