We have tried very hard over the years to treat all of the teams the same, and not have a single team that gets most of the attention or all of our best kids. There is nothing wrong with other gyms doing that, it just goes a bit against our philosophy for our gym. That being said, our goal in setting up the teams is to make them roughly equally strong for their division. (note that this is different than saying that all of the teams should have the exact same talent as each other.). Some divisions are traditionally stronger than others, so our teams in those divisions will start out with a bit stronger initial rosters.
Putting rosters together is a very difficult and time consuming process. You ideally need the right mix of bases, back spots, flyers, jumpers, tumbers, dancers, and performers on each team. Depending on the size of the team, you can also afford to have a limited number of "specialists" that are exceptional in 1 or 2 areas, but do not necessarily match up to the others' skill set in other areas.
We simply do NOT take the best 20/30 individual athletes and put them on one team, then put the next 30 on the next, etc. . . We don't feel that works with our philosophy. Also, there is often confusion/frustration from some parents because they focus almost exclusively on tumbling ability when comparing athletes, while we tend to look at a much bigger range of skills. They think that because Suzy can do a better running tumbling pass than Jane, that means that Suzy should be on a "better team" than Jane. They may be correct about the tumbling (although they are often NOT correct), but they simply do not see the overall picture. Jane may be a beast who is 11 inches taller than Suzy and the team absolutely needs another back spot to be able to stunt. That skill helps the team more than Suzy's extra tumbling would.
I compare it to (American) football. A successful football team will have a surprisingly wide variety of body types and skill sets. You may have a 6' 6 300lb kid who can't catch or run a sprint to save their life, but can absolutely bulldoze anyone on the opposing team out of the way. You may have a kid who is only 5' 8" and 175 lbs, but who can absolute blanket any wide receiver to where they never get open. Then you have your kicker, who at times could be your most valuable player, who looks like someone who should never set foot on a football field but be able to nail any field goal from 55 yards and in with no problem. If you simply put your 11 "best pure athletes" (or 11 fastests, or 11 strongest in the weight room, etc) on the field every time, you would probably get destroyed by every team you faced.