So, you've never seen a child beauty pageant, but you think those bringing it up are covering the pornographic aspects by comparing this to them? Stripesgalore, people have been discussing the pornographic and pedo issues within pageant circuits for decades for good reasons.
Beauty pageants are done singularly, so the latter could not happen. Smacking one's own rear and suggestive rubbing, yes, that happens in pageants with a dance/talent components that can include dance. Both happen in certain types of group dance classes, the ones aimed at being 'commercial'/build up to a professional career outside of classical/traditional dance.
When I was the same age as the girls, I was in a multiple dance groups. We listened to the comments of the judge, and one of the complaints with one group was that our skirts were too long (while boys wore trousers). Skirts barely long enough to cover the short-shorts that were on display after we stripped off the skirt towards the end of the routine. At that age, I was also doing hip-hop dance, with all that entails in modern popular culture. This was all done with heavy encouragement by my mother and community, my mother was big on teaching me popular what could only be described as sexual moves and associating them being able to be financially secure in the future. Any failures was just me being an ugly fuck-up and when I had to drop due to overtraining injuries/juvenile on-set arthritis (as it was called then, not sure about now), I was told 'At least you have enough training to be a stripper'. I was not alone in this.
Maybe instead of disregarding the comparison to other aspects of girls being training for media and other success through encouraging/pressuring on early sexualization, it could be acknowledged that all these things are connected and those with old roots or are seen as girls having fun is just as dangerous as when directors get involved in the process. All the girls auditioned, it's likely most if not all had dance training involving all of this prior to this movie being an idea.