The legal form doesn't determine whether something is state owned or private.
So, sure, you can have a rail system self-fund as long as you let it build whatever the fuck it wants at stations and funnel all the profits back into the train line.
I agree that there are many big businesses bureaucracies but they tend to be in areas closely linked to the state/government because of heavy regulation: banks and insurance for example. They tend to survive despite their terrible efficiency because it is way too costly to enter their business for a small actor. Any of their real competitors is already big enough that the bureaucracy is already well established...
Being a bus driver used to be a decent job for semi-retired construction workers, and such.
But then privatization hit, and over the last 20 years, there is no niceness left. They're even trained to disregard customers, and penalized otherwise. It's insanely inhumane.
And the causal effect is very clear, there can be no doubt about it. It's not the bus driver's fault.
Honesty, it's German politics doing precisely this that's part of the problem: flippant diagnoses too broadly applied from afar.
The more focused a company is (the more reliant it is on its core service) the more accountable it can be. I'd argue many companies are if anything more accountable than the government. It doesn't have to be true, but I'd argue it often is.