But aren't you still dealing with the worst of humanity or a close facsimile of it, in a daily basis
Not even close.
While I was in college I had professors who were current and former police officers/detectives/deputies/ADAs and the stories we heard made it clear what kind of experiences we would likely encounter in the job.
As a driver, what do we encounter that's so bad? A receiving clerk who's got a bad attitude? I am very professional on road so I can usually make good of every situation so it's never a big deal.
The majority of the stress I encounter as a driver comes from preload not having our truck loaded which holds us up in the AM, Dispatch's bright ideas, and management running you around after you're almost done with your run.
At no point am I worried about the possibility of taking a life to protect mine or the life of another's.