In an ideal team, all players have equal abilities and skills, and are all playing to their abilities on the night. All players have the right to equal court time, but there are too many factors associated with court time.
Like people have said, training is where it all starts. If players are not turning up to training, or putting in at training to develop skills, or not following coach's instructions, then they must expect less court time. Kids develop best at training where they can be talked through and shown what they don't understand.
The other issue is when coaches have their favourites. I have seen this where kids have poor training attendances, low actual (not perceived) skills, poor teamwork, but show all the "correct" body language and have the coach's ear for some reason. The coach overplays them and this spreads like a cancer throughout the team.
Bottom line? I believe that court time should be more "situational" based on the game rather than prescriptive, and the best team should be on the floor as much as possible. That best team varies according to the situation. It is up to the coach to develop skills and it is up for the player to commit to the team and make the most of their development opportunities. From the player's side, commitment and discipline drives court time.