I think changes are needed. Ainge and Stevens have both been around too long. Ainge for one hasn't made a good trade for ages, and Stevens' teams seem to lack consistency--a sign that they lack discipline and don't know their roles--if they have been given any. The Celtics have evolved into a very Un-Celtic team. Not as bad as the Gaston era teams, but not as good as the pre-Gaston teams and those Ainge teams coached by Doc Rivers. The decline was deliberate in a sense, since the team had to rebuild because of cost constraints.
Ainge has been too conservative in his trading and FA approaches in recent years, and it has cost him. Rival GMs have been much more aggressive and have improved their teams more. It appears the coach has been given a free reign to do as he pleases, over the years, and was more successful early on with lesser teams. He also was given a lucrative long term contract, recently extended, without any prior NBA coaching experience. That has not been a formula for coaching success in the NBA. They might have been better off with a McHale or other Celtics alumnus who was familiar with the Celtics formula for winning. Rather than a coach who was confined to what worked for him in college.
So where does the ownership stand on all this? My impression is there isn't much concern--there is little pressure to win. Wyc has his title. It's now simply a question of fielding a good enough product to put fans in the seats. TV revenue takes care of itself.