I don't know how Deutsche Post ended up on this list, I've rarely had issues with them, certainly much less than with any of the private delivery services (Hermes and DPD are absolutely terrible).

When complaining about the quality of the "former state railroad", the emphasis is on "former". The Deutsche Bahn offered much better services, more efficiently and at higher reliability, when it was still state-operated.

Telekom has always been bad, of course. To be fair, some of it is due to bad regulation, but they also just seem shockingly mismanaged.