I am a high school football coach in upstate NY. This is by no means acceptable. The general rule of thumb, at least in my area, is you play like you normally would until halftime. In this particular instance you could've completely subbed after the 1st quarter. What you wrote demonstrates to me the coach knows how to lay off. He scored 83 in the first half, but only 23 in the 2nd half. Clearly, the coach changed things, but it should've happened after the first quarter.
In a blowout game like this you have the opportunity to work on things you might not normally work on. Different blocking schemes, punt team, try different players in different spots. All of those strategies would've limited the scoring without risking a loss after the 1st quarter.
I agree with your synopsis. This is utterly classless.