I think Gabi on TG is a perfect example of a smaller athlete who has earned her spot. She has technique, form, the whole package. Do some cheer squads put girls in the air who only got their because of their size? Sure. I'm not denying that. But it's a coaching decision, and one they have the right to make. If you don't like how they coach, find another gym.
I also think sometimes parents have a massive case of "Susie's Mom" when it comes to the position their daughter has in a stunt group. I am so sick of hearing parents complain about how their CP should be flying but the coach wouldn't give them that chance. The coach makes decisions based on the team as a whole. Even if your child is flexible, it doesn't mean they have the air sense/body control to make a good flyer. What is wrong with being a beast back spot/base? If 8 stunt groups are going up, and your daughter is the 9th best flyer, she's not going up. If you are dead-set on her making that spot, let her take a stunting class to improve her technique.
Blaming these decisions on size alone isn't always an accurate reflection of why the coach made the decisions they did. Not every child is going to be a flyer. And flyers don't happen without backspots and bases. Backspot/basing doesn't mean you're any less important to the team. Quite the contrary. You are every ounce as important as the girl pulling a scorp in the air. If you have questions, schedule an appointment to POLITELY discuss your questions with the coach. Be prepared to listen, and if you're doing more than 25% of the talking, you're not listening to the coach enough. You might be surprised what you hear. Maybe Susie has a fear of heights, turns into a noodle, or maybe it's her attitude keeping her grounded.
Bottom line is this, if you don't like it, don't cheer there.