I don't know about other states but in VA, cheer is first and foremost about cheering games. Competing is only within the state within a set period. 2 rounds of districts, regionals, then states, all done by the first week of November, season starts in August. Before districts teams can attend VHSL sanctioned invitationals, to get your feet wet. We did 2 comps prior to districts my senior year and it honestly felt like we had a full comp season. All-Star isn't an option everywhere.
I think to balance a full comp HS squad and all star career is to consider the culture of the town. Are many girls in your HS program on super competitive L5 teams? Maybe you cut your comp season in January. Is HS the only option? Then make your school full season comp. Is it a mix of both? Then have the option. Gyms can try and work to plan smaller locals around HS if they have a lot of athletes from one HS on their team.