I have done a couple of shifts delivering for DX. It is almost impossible to do the job as quick as the depot supervisor wants, to get all your drops in etc. You are expected to offload items which are clearly 2 man lifts (individual items way over 50kg), the van will have been loaded by a warehouse operative who is having a game with another warehouse operative about who can make life most difficult for the driver – it’s a thankless, soulless existence.
You are driving on the limit, the depot is constantly calling you, addresses are sometimes hard to find, traffic gets in the way etc.
Not making excuses for crap service per se but having experienced it myself I am a little more tolerant of the actual courier. It is the firms who should be blamed for it is they that determine the working culture.