To your point, while all positions are up for grabs and must be earned that does not mean that all you must do is out play someone to earn the position. Often there are other less tangible factors.
I have seen the gamut in my brief time with my DD and I have trusted my assessment of the situation each step, as a result she is in a situation where she is treated fairly. Fairy does not mean that she gets to play her preferred position all the time. DD is playing on two teams right now and both are fair for her abilities within the context of each team. One team is significantly better than the other. Fair means that if I look at the book on the games, her place in the batting order is in line with her stats (7th on one team and 4th on another) and when I look at fielding (every inning on one team- sitting half the non pitching time on another) and pitching (about even) , her playing time is in line with her performance and where she stands relative to other players on each of these teams even though her role is vastly different on both. On one team she is a core player, on the other she is expendable. That is not to say one situation is better than another, they are just different experiences. One thing I know is that on the better team, if DD outplayed the girls ahead of her then she would win the spot over time. That is ALL you can ask of a coach.