Talent - They don't have the quickness, the gift of length, the ability to create their own shots. They don't have a next level offensive player (s) that has (have) the ability to score on their own outside of any structure, in transition or secondary transition.
These are things that can't really be taught, but can be molded if a player or players have it.
Yes, even one player can make a massive difference. Two definitely can. If you have a Terry Rozier that can go get buckets on his own, this makes the game easier for all his teammates. Just one example. Outlet pass to Rozier he is going from half court to the rim in a blink. Or he's taking a solid pull up jumper off glass and either nailing it or his teammate is in position to go get the rebound. He's that good. He has the handles, the skill, and the length to get his shot for himself or give it to a teammate that has the ability to run the floor, catch a lob or go get the rebound (Trez) and throw it down.
Picture the outlet pass to Locke. He has Withers running with him. Or Cross. Or Dre. This is not Rozier/Harrell on the break attacking. Locke and friends just don't have the talent to do what Rozier and Trez could do. Or if that pass is to West. West just does not have the quickness to get from Point A to Point B where he wants to go, etc.
Same thing when your shot clock is running low and you need something to happen in half court.
You are't seeing high end basketball because you don't have high end players.
This is just a snapshot example of what, IMO, the program is missing right now.