Honestly, sounds like a bunch of whiners on this board. It is good that we all have opinions on our favorite players. Fortunately we don't know as much about them as Danny Ainge and his group who have worked each player out and scouted them extensively.
You don't like the 19 year old picked? Guess what, he could be much improved by the time that he gets any serious burn. Look at guys like Tyson Chandler, Biyombo, Chauncey Billups, etc. They all took time to develop, but have each contributed to playoff runs. There's no reason to believe that Jaylen Brown can't contribute in the long term.