Yes, cheer should be considered a sport. Most of the cheerleaders at our schools are high level gymnasts AND skilled dancers. No they are not a dance team and there is no "some gymnastics" thrown in. Its quite a bit. Their sport takes just as much skill and practice and training as football, baseball, basketball and any other sport.
Are they mean and snobby? Well, dd learned something about this in high school. Dd was in cheer when she was young but then quit to go on and do other things. Several of the girls she was close to stayed in cheer. When they got jr high age, they sort of drifted apart since they were busy with cheer and she was busy with show choir. Well, she accused them of being snobby because they only hang out with other cheerleaders. A lot of the kids accused them of being snobby for the same reason. In high school, the kids are required to take a performing art so several of the cheer girls decided to join choir their sophomore year and auditioned. The choir girls rolled their eyes and dreaded having them. Well, come to find out they all became really close. When asked why they only hang out with cheerleaders, the choir girls were told "because no one else will hang out with us, they think we are all snobs".
Are they spoiled? I am sure some are. So are some football players and some choir kids and some band kids and some chess players, etc. etc. etc.
As for Disney no, but I have during a music competition. Mostly younger teens. They were ALL brats, including my own. Its just the nature of the beast (teens) it has nothing to do with what activity the do or sport they play.