In that time in the office, he's doing trip requests, balancing accounts, checking paperwork, coordinating middle school visits, managing the lesson staff, and everything else.
A HBD isn't just a teacher, they're a coordinator. Same as a head football coach.
But, as others (and you) have said, if you're not willing to put in the work, find another profession. You can make a great living as an assistant band director. Maybe some of your friends are hired as a paraprofessional (because they're not certified, or because that's how the district pays their perc tech) and so they get paid less on paper. If you're not willing to start at the bottom rung, employment isn't really going to work out well for you in the public sector.