The closest comparison I can think of for Boogie is a young Zach Randolph. Young Randolph was insanely talented, immature, selfish, and cancerous in locker rooms. Here's a per 36 comparison of the two during their peak statistical seasons:
per 36 min Pts Fg % Ft % OR DR TR Blks A/T
Cousins age 24 25.4 .467 .782 3.3 10.1 13.4 1.8 .82
Randolph age 25 23.6 .467 .819 2.9 7.2 10.1 0.2 .69
It was 3 trades and 4 years later that Zach Randolph was ready to contribute to an actual contender and even then he was surrounded by other all-nba caliber veterans in Mike Conley Marc Gasol and Tony Allen. As recently as last year he cost the Grizzlies a playoff series against the Thunder when he was suspended for a crucial game seven for punching Steven Adams.
My point is that some guys have the skills but not the mental makeup to be the top guy on a team.
The other downside to these guys from an asset/trade perspective is that they lose value at every stop. Zach Randolph was traded for considerably less value with each successive trade, as would be the case with Boogie if the Celtics acquired and then attempted to move him.