What they fail to mention is that those two aspects were broken up initially by the government after privatisation in the first place because the accountability and running of both aspects simultaneously was so bad.

Network Rail which the GP was mostly talking about isn't privately owned.

Rail Track, its predecessor was privately owned but it collapsed in 2002 after the Hatfield train crash. Following that it was bought by the government to create Network Rail.

The thrust of steve_gh's argument seemed to be that decentralisation of that (publicly owned, as you are noting) body, and particularly alignment with the train operating company regions, would improve the situation.

I wanted to get their views on any industry-specific constraints around the orthogonality of "centralisation" and "ownership", because I feel like they are too frequently conflated (not by anyone in this thread, to be clear), despite not being inherently linked - but there might be some good reasons for that in the context of the current state of the British railway network.