It's a graded, judged competition held off site. It's not a practice, it's not a rehearsal, the kids are being ranked and scored. Just because they don't "advance" does NOT mean it's not a contest. Contests are 100% extracurricular. That's why UIL C&SR is now an "evaluation" and not a "contest" per the rules.
Concert is a totally different animal than All-Region. There is no TEKS to justify 100% mandatory participation in all-region band. There are TEKS that justify participation in C&SR.
Finally, if your kids ever have to pay to enter, it's 100% a contest.