If that admin also is supportive financially. Bad equipment and lack of external education factors can be overcome at the district level. Supportive instruction, (district positions to have enough staff to offset loss of private lessons, bringing in those master-class folks at district expense, etc.), is also critical in those lower SES areas.

I was in a lower SES for decades and a supportive admin was critical. I agree. But not just in keeping parents in check but also making what physically goes on the field or the stage level as well. When schools are spending 100k or more on a marching show including extra guard and marching techs, dance instructors, body movement coaches, custom writing, specialized props, etc., it doesn't matter how supportive the admin is if they don't offset those differences. Stage is totally different and is much easier to level out for low SES with a few quality instruments and good teaching.