CJ could play well with scrubs because he's a ball dominant scorer, and could display his talent no matter what the situation.
Collins isn't someone you throw the ball into yet. When he plays in garbage time, that's what happens. He is someone that would play better off of the starting lineup. He and CJ are talented on different ways.
Collins is also 19, CJ was 22 his rookie year.
Collins isn't "MILES away from cracking the rotation". He's already a good defender, and all he needs is more strength to be a rotation player. Combine that with improvements in other areas and you have a good all-around player.