If you look at many of the bigger gyms, their most recognizable athletes are those that have come up through their system. They didn't just waltz into the gym 2 years ago and get handed a center flyer/last pass/etc spot on the gym's most recognizable team. In fact, I would venture to say that MOST of the level 5 female athletes on world champion teams have cheered at those gyms for 5-10+ years. It's a reflection of those larger gyms' farming systems (aka: their lower level teams). There is no such thing as a gym that has strong level 5 teams but only sub-par lower level teams. If a gym only pays attention to their top level teams, they won't have anybody to feed that team(s) in 2-3 years.
Have there been teams that won a tight race because they wear a certain uniform? I'm sure of it. But just the opposite can happen, also. A big gym can lose because their known teams are SO GOOD that a judge/spectator can look at their unknown teams and be extremely underwhelmed. For example, if I went to a competition and Rays Junior 3 team jumped like everyone else in the division (assuming those teams jump averagely), I would be disappointed. It's something they are known for and excel at so much on their upper level teams that I would expect the same attention to detail with lower levels. Every other team could jump just like the Rays J3 team and I wouldn't think twice about their jumps not being executed well enough. (P.S. I used that example because it's not the case. I think Rays lower level teams have always been a large gym that holds their own weight in any level they compete.) It happens on both ends of the spectrum, and personally, there have been very few times when I was truly just dumbfounded about how the judges came up with the winner. Most of the time judges pick a fair winner.