Are they teaching their classes fully?
Are they covering the AP Music Theory class?
Are they covering any other classes?
Are they the department chair?
What about all the extra administrative duties that you don't necessarily see or are involved in?
The head directors hire the people they can trust to take care of the kids not in the top ensemble.
Your estimated money differences seems like a long way off.
Are there bad head directors? Sure.
Are there great head directors? Absolutely.
Always do your research before you accept a gig.
That's my $.02