Kanter is a very productive big man. He will help you win regular season games.
In the playoffs, he can still work for you in certain matchups. The Blazers needed him against the Nuggets and he did good work.
Still, there's only so much value he can provide you. For $5 million and 20-24 minutes a night, he's solid.
If the Celts had championship aspirations this year, relying on Kanter to play significant minutes would be a problem.
As it stands though, it'd be an amazing turnaround if the Celts were as good as the Blazers next year.