I don't think the pick is an overpay for Butler, but I'd much rather acquire someone like Anthony who will cost far less to acquire and provides as much if not more offensively (though considerably less defensively).
I can't believe I'm saying this but I'm leaning this way too, and if we play Melo at the 4 he's played reasonable defense there over the past 4 years. We could have the best of both worlds holding on to the Nets pick. I haven't looked at it has stats very closely, but I think he is a little more of team player with passing than his younger days.
I really don't get where Anthony got the ball stopper reputation from. He has always been a respectable passer. Slightly lesser than Pierce at their respective points in their career, but Anthony has been a better scorer than Pierce at their respective points in their career. Also, while Anthony had a bit higher USG than Pierce, he has turned the ball over a good deal less.
Anthony is one of the best pure scorers in league history. He can post people up, take people off the dribble, and hit long three pointers with hands in his face. For a SF he is an excellent rebounder and a respectable passer. He turns the ball over very little for someone with the ball in his hand as much as Anthony has it. And while he doesn't give full effort defensively a lot of the time, in large part because of his offensive load, he is respectable enough defensively when he needs to be and puts in the effort.
Anthony would be a near perfect small ball PF for this team. He provides the missing offensive dimensions the team needs and can't really be much worse defensively than the current team, especially against the quicker more perimeter oriented PF's that Horford, Johnson, and Olynyk really can't guard anyway.
So for me, while Butler is a better all around player, I'm not sure he is really a better fit, and he would certainly cost a heck of a lot more to acquire. At most Anthony is going to cost Brown and salary filler, at most. He might just cost salary filler and some future late firsts. Seems like a pretty clear no brainer to me that Carmelo Anthony should be a Boston Celtic.