Hmmm. Look at the IEP programme for a jaw-dropping example of what happens when a contemporary alternative approach to leasing conceived by the state is taken. [The only upside is that Hitachi are on the hook for the enormous cost of fixing the metal fatigue failures on these things]
What's the common denominator? That the counterparty (the state) is habitually incapable of doing anything competently and with enough acumen to not end up having rings run around it.
There's nothing wrong with ROSCOs/leasing in principle, essentially the model just distills down to another way of packaging insurance. However, unless they are short term anomalies, profit margins like this are all the evidence you need that the other party to the contract doesn't know what it's doing.
The problem over and again is the DfT. Given the long-term nature of the issue, it really is the DfT rather than governments of whatever stripe. It's a bit like the equivalent of what happens with every government IT project, ever, except on rails.
How anyone thinks putting them really in charge of everything rail via full nationalisation would make things better is hard to comprehend.