How many all-state auditioners advance even TO, let alone past the region level on a bell kit? How would you even practice the four-mallet audition?
Nearly all music written for band at the Grade 3+ level has marimba parts these days. If your kids can't play and navigate a marimba, they're not prepared for band life after their second year, realistically.
If we aren't setting kids up for success, what are we setting them up for?