i personally don't agree with your opinion, but we're all entitled to our own.
FIRST is out there to get students excited about science, math and technology careers. The best way to do that is by showing how much fun you can have doing it. Who really wants to go end up in a job where they're not going to have any fun at all? Most people don't.
There are actually some awards that are based off the numbers (highest rookie seed award) but the majority are based off of how well the team presents themselves and tells their story. Which you end up having to do to get into both college and a good job. --> very important in the professional world.
As for the "costumes" many of the things i think you're calling 'unprofessional' are mascots and cheerleader type costumes. They're made for the sole purpose of cheering their team on, just like football and most other sports. As for shirts and jerseys, it makes finding the other students on your team ten times easier, especially is a crowd of thousands of students. Remember in kindergarten, when you had to wear a specific shirt to go on the field trip? same concept, but also so that other teams can recognize where you're from.
MC's -like a DJ at a dance party, they're meant to entertain and keep people excited and moving (back to the point of not making things seem boring)
also, maybe you didn't have a good experience because you spent the majority of the time playing a video game
i agree with most of the others, you should give FIRST another shot, an open mind is the best kind to have.