I'm not sure that's a testable hypothesis. Yes, having (way) fewer people would prevent most climate change, pollution, etc issues. However the trend is always

I'm not sure that's a testable hypothesis. Yes, having (way) fewer people would prevent most climate change, pollution, etc issues. However the trend is always that humans proliferate until a point where it's not possible to feed them. The plague didn't stop human overpopulation. Even the worst king doesn't stand a chance. Exception might be complete destruction through nuclear war. But that wasn't available to Richard III.