It's the other way around. Moving up the DH-hierarchy doesn't make people less mean. It's just that less mean people have a tendency to move up the DH-hierarchy. This is based on my personal experience. Since you're the one making the original statement without supporting evidence, I feel that the burden of finding evidence should be on you, that's why this isn't a DH3-statement, but DH7. ;)
Thanks for the read.