Sure, he's a great player, a box score stuffer, a legit all star. But it took until his final year of Jazz contract control to finally get where we knew he could be. It was slow enough early that the Jazz weren't 100% sold he would get a max deal as A restricted free agent (a clear mistake). He wasn't a clear all star until year 7. I think we'll look at his career in a few years and see that he peaked in his final season with Utah. He'll have some good years in Boston, but never hit the level he played at last year.
Mitchell has length, speed, athleticism, skill, and moxy. His career at will be a much faster rise than Hayward's. He just needs to stay healthy and he'll be all star caliber in two years. He's got a great opportunity with this team. Great defense where he'll play a key role. And an offense that will give him plenty of opportunities to develop.