Also Ainge didn't have to let him be a UFA.
He could have held up the deal and made him an RFA this year, then offered the $9m QO. That might mean Green takes the QO and bolts in a year, but you'd have his Bird Rights.
I think the reality is for better or worse, Danny is in love with Jeff Green - must be a scouting thing, because the stats suggest he's not this good, and I think the market for Green was lower than $36m / 4 years.
That being said, if 4th year is team option, then I'm fine with the deal. There is some value to having a few role players making more than the minimum, as it creates more trade options. And there won't be cap space net three years anyways. Although if they run into the Apron because of it, its a problem.