I think most people would agree that taxpayer value for public expenditure should be maximised, and were the money from the licences going directly into the public coffers then we could certainly have a discussion about whether taxpayer value is maximised by selling the data or giving it away for free.
That, however, is not what is happening here. As so frequently happens in the UK, the data is publically funded, and the profits are privately realised.
I agree that large-scale API provision is added value, and I have no objection to a private company making a profit from that. What I object to is a private company being handed a monopoly on that private data, with no effective oversight being given to the terms under which they provide access to it.
ATOC, by dint of the exclusive licence granted to them by Network Rail, have complete control of the market for this publically-funded data. They are adding value by serving it as a reliable API, certainly; however the price they are able to command has little relation to that value, because they have no competitors.
* sorry
If you believe that the correct way to maximise value is to use the data commercially to maximise revenue then you won't see a problem with the current situation.
If you believe that the correct way to maximise value is to provide the data for free to end users then you'll think it's wrong.
The article implies the latter is true without argument, and implies it's the norm in the UK.