DHL is bad because they underpay their employees so in a large city, employees will dump their packages at the first door, very annoying if you life in a large house with many flats, you have to search for the person who took the parcel - even if you're there they will not ring the bell, just dump everything.
Deutsche Post next to me you usually wait 30+ minutes in a long line (dozens of people) with the unfriendliest employees possible, it has a 1.9 (!) rating on Google.
(I have no car) Deutsche Bahn is incompetent, trains cancelled, too late, wrong car order, non working climate control, 1st class car missing, restaurant closed and much much more.
Deutsche Telekom wouldn't activate fiber for nearly a year although everything was build and finished. Computer said no, no one wanted to come and see that everything is ready (they installed everything) because the computer was in an inconsistent state (20+ calls plus a lot of escalation worked after nearly a year of me paying 99EUR/month 5G for my remote work).
The others pay worse, then. DHL has by far the best delivery for me, closely followed by Amazon, then it’s UPS (though they are used so rarely, my samplesize is tiny), and finally DPD and GLS. Oh, and of course there is "roll the dice delivery" aka Hermes.
Deutsche Bank is massively worse than any of them for society and to most customers. Vonovia is a stain on society. No doubt there are many many worse companies for various reasons than the three you listed.
Deutsche Bahn is inefficient. But I have no idea why you consider them all that terrible. Deutsche Post isnt even all that bad. Theyre one of the best companies in the public package delivery space.