There is a great video on Youtube of Allen Iverson saying he doesn't understand how he could make his teammates better by practice. What matters is games. His presence on practice doesn't effect what his teammates work on or develop.
Contrast that with Kobe Bryant, who said he thinks the only reason they didn't win the championship in the 2010-2011 NBA season was that he wasn't able to practice with the team and keep the intensity level high. He wasn't able to "crack heads together" to get people up to the level they need to be at.
Allen Iverson: 0 Championships
Kobe Bryant: 5 Championships