You certainly develop in practice, but the vast majority of that development is through teaching, not competition. There are only a few minutes of pure competition in an unstructured setting (like a basketball game) during practice. It's only snapshots of what needs to be worked on for the team, not the player. So you need to play. You need to play to get the film needed to show what needs to be corrected. You need to play to feel the stress of needing to perform in front of fans. You need to play to feel the speed of the game when your opponent has 5 guys playing hard while also looking to execute. You need to play to learn how to adjust when the opposing team is game planning against you specifically, trying to take away what you do well. Show me a player who is immensely talented on put them on the 1992 Dream Team and I guarantee you they develop more if they played elsewhere where they get 30 min/game and are relied upon. The world's best practice will always fall short of an average competitive game