I disagree with the notion that all gymnasts from the same level should be getting the same hours, same training and so on.
First of all ability may not be the only thing the coaches are looking for when placing kids into the A and B groups. Things like effort in training, Committment, attendance etc may also play a role. Often the A team look like they were chosen just because they are better gymnasts, but they may be better gymnasts because of those other factors mentioned. If you have a group of students who are making the most of their hours, training to their full potential, putting 100% into the hours given and attending each session, then increasing hours can be an option. If you ahve students who are not fully using the hours they have ie absent a lot or not putting in 100% each session, it makes no sense to increase those hours.
Secondly different groups may have different ultimate goals, which means they have different training plans. The A group kids may be the ones who show potential for possible elite, to make this happen it means they need a lot more hours, high levels of strength training, a lot of up training on skills etc.
If you train all your gymnasts in this same manner, then you are likely to burn out some of them. It doesn't work for everyone, if the athlete is not destined for elite, then you don't need to put their bodies on the line in this way.
It is like TOP's training. Is it a great tool for gymnasts? Sure. Is it something that should be for everyone? No. TOP's requires hours and hours of conditioning. It will be hard and it will be painful. Invite the wrong athletes to participate and their joy for the sport decreases.
The other notion is that gyms that do this may also very deliberately be creating the resentment. The idea is not to create unrest between parents and teammates (although this can happen, and it's not nessesarily a great way to create success). But to create desire. The B team kids may be jealous of the A team kids, some kids will use this jealousy to step up their game to push to be selected for the A team. On the flip side, A team kids and parents probabaly enjoy their status and have a little fear of losing it. Which may keep them committed and working hard to avoid being moved down to the B team.
To top it off, equal level does not mean equal ability. You have level 5's who have all the level 5 skills to perfection, can do all the level 7 skills and are ready to work level 8 skills, and you can have leve, 5's who have just barely learned the level 5 skills and need a lot more work to train them consistently before advancing. These kids may have the same training level and the same competition routines, but that is where their training similarity ends.
Our kids are growing up in a world of instant gratification, everyone gets a trophy for participating and yiu can have whatever you want. One of the reasons we want our kids to do gymnastics is because it is not like this. You can't get out your credit card and buy skills and results. It takes time, effort and patience to learn gymnastics. It has it's ups and downs and sometimes it's painful or scary or difficult. But gymnasts push through because the rewards for their hard work are so wonderful, this teaches them incredible life lessons. Do we really want to put them in an environment where privledges are doled out on a basis of equality rather than effort.