Coach's greed is the answer to every problem and question. See if this does, or does not make sense.........
Generally speaking, coaches are pretty good at assessing a child's physical gifts. When it comes to mental, emotional, and personality traits, the assessment becomes less exacting, and in some cases appallingly absent. Staying on track with this thought, let's say a coach has a good sense of both sides their gymnasts. Keep that in mind for a moment.
There are many coaches that take pride in what they can do with the raw talent (both mental and physical) that walks through the door. They have a personal and professional interest in getting it right when they choose kids for a group. Add that notion to your to your keep in mind basket.
Some, but not most, of these able and proud coaches feel responsible for every child, they've invited to their team, regardless of their level of "gift". These coaches would gladly clone themselves and add whatever possible to their facility, just to make sure that nobody gets forgotten, missed, or left behind. Hold on to that idea just a moment while........
Many coaches, more than some but less than most, also feel an obligation to provide for every child while conducting a program to accommodate those with extra potential based on their cumlative gifts, and will do what it takes to preserve that opportunity for those who need one.
Bringing it all to one cohesive thought......... I hope!
How in the world can a parent, who has any measure of respect for the program they chose for their child, believe that the coach has an agenda that purposefully over looks their child. A coach can see all the physical traits exposed by a child's current skillwork, and know what they need for the next 6 to 12 months. Sure, there's the rare "breakout" of greatness, but those kids are easily noticed and moved as soon as sensible and possible.
Really...... What purpose could possibly be served by leaving a child behind. To do so would give a coach one less opportunity to show their abilities to the rest of the community. So the next question......
Why not move them all up to the top group and have them work identical hours with identical coaches. Look at it this way. Team gymnastics in a quality program is a lot like an all you can eat buffet, as opposed to dim sum. One puts everything out and allows each person to consume what they can. Those who have greater appetites get more for their money, well sort of, because what they get is a dining experience that provides them with all they'd like. So should the people with smaller appetites complain they weren't allowed to eat the same amount and enjoy as much as the other person. I'd hope not, because if they were to do so, they'd likely have an unfortunate reversal of desire. If you get what I mean......
Advocating for your child is great in areas like desire, personality, illness, and burdens place on a child that manifest outside their gymnastics experience. Asking questions to stay informed, or to know what you need to guide your child are fine also. Beyond those two areas, and assuming you chose the right program that features the type of team your child wants to be a part of, there's nothing else to do but drive, drop off, return, and pick up...... repeat as needed until your child becomes the gymnast she can be..... maybe even the gymnast she dreamed of becoming.
My sincere advice is to not question the coach, and to leave your child out of your frustration loop. If there are any questions, they should focus on the program's top to bottom capability of helping kids do gymnastics. If they do that well, then stay. If they don't do that well, find a gym that does. The last thing you should do is to create changes that benefit your child without making things better for every participant, including the coach.