Convincing athlete to commit to robotics?

[Ed Law]

Creating a list of each choice like you did is a great way to see things clearly. You may want to talk to your friend that he is missing one point. In general colleges do not like to see people quitting things in the middle of their high school career especially their senior year. Getting involved in high school sports is not all about winning. It is about making a commitment to others, training hard, doing your best, trusting your teammates, sportsmanship etc. Whether he is on a winning team or not does not matter especially if college basketball scholarship is not involved in this case (which is my assumption because otherwise he definitely cannot quit). Some colleges like to have students who were involved in sports. They never asked what your team or personal record is on the application unless you are being recruited. The common app does not even distinguish between varsity or junior varsity teams.
Your friend is already on the team. Trying to convince him to quit basketball to concentrate on robotics to help you and your team may not be in his best interest. He can still benefit from FIRST even with minimal involvement. He can still be inspired to go into STEM. But like other people have already said, it should be his decision. A good friend will help him make the best decision for his future, not yours.