I legit think that scoring forwards who don't create shots for others and play meh defense are some of the least valuable players in the NBA. The ppg end up looking good and artificially inflating their value, but they do not help their teams win.
I will admit, the one thing Collins has going for him is that he's become a 43% three point shooter, but its only on 3 shots a game. He doesn't really stretch the defense out throughout the game. He can score off of other creators at a really high level, but most NBA forwards can score off of other shot creators. The additional efficiency Collins brings is nice, but it's not so much that it raises a team's offense significantly.
But then if you sign him to a big contract and he's averaging 17 ppg, you've got to get him the ball. The problem is that he doesn't create for others. He's figured out the little dump off pass to Capella on his rolls with Young, and he can occasionally hit the corner guy on those rolls, but he doesn't make his teammates better on offense.
Then you have the problem on the other side of the ball. Scoring forwards like him often stay lighter so they can drive to the basket, but that means they struggle to guard centers. For whatever reason, these scoring forwards are often really bad at staying in front of their man when they drive and rotating to the help their teammates.
So having a player like this caps out your offense because you have to give them the ball even though they don't make their teammates better, and you have to gameplan around their defense because of miscues and their poor flexibility.
If you want a little more scoring at that position, I think you can get rough approximations of what Collins brings offensively for much cheaper like Kuzma, Anthony, Green, Bagley, Barnes, etc.
However, I think it's more important to have low usage guys with defensive versatility at that position (if you have your top two scorers/shot creators already) in guys like Al Horford, PJ Tucker, Jae Crowder, Robert Covington, Larry Nance Jr., or even a guy like Grant Williams.