You've done everything except talk to the one human being involved who appears at your residence every single day. If I was your letter carrier and knew you felt this way I'd honestly be hurt that you didn't bother to ask me about any of it.
> the organization could use some serious cuts
Miss the part about them being the backbone of package delivery in this country? Or the part where there's nobody to replace them? Well it doesn't matter since the USPS is financially self-sustaining.