The contract requires Agility Trains (the holding company) to supply and maintain the trains, and penalises them if they cannot provide above a certain number of usable units when they're required. They carry a lot more risk than a 'normal' ROSCO.
But the penalty isn't anything beyond the leasing charges not being payable. In other words, the lessee only pays when the asset is provided in working order.
Now of course, that is different to how most conventional train leases work - but the availability isn't really any higher under conventional leases. The reduction in payments on the handful of occasions that working trains aren't provided by Agility Trains, is more than outweighed by the ludicrously expensive leasing charges.
To use your car leasing analogy, it would be like leasing a car with a guarantee from the lessor that it will be available for use 99.5% (or whatever the actual number is) of the time, and that if it breaks down and can't be fixed on the spot they'll not only replace it but compensate you as well. In return for this guarantee, the contract obliges you to make the car available to the lessor's service centre at certain intervals so that they can inspect it and perform any required maintenance.
Well not quite - firstly because the availability is more like 85%, and secondly because the 'compensation' is limited to a discount off the bill that would otherwise be payable. So more like a refund in reality.
Now, of course, that sort of guarantee probably warrants tighter terms around the rotation of units and how often they return to a depot capable of undertaking repairs. But the terms that the DfT agreed to mean that this box is 'ticked' so long as the units are returned to an approved depot every 24-48 hours, even if that depot only has servicing facilities, but no maintenance capabilities (on the 80x fleet).
Clearly, this term has little to do with ensuring the reliability of trains (and minimising leasing fee 'refunds'), and more to do with guaranteeing a future ability to extract £££ in exchange for a contractual variation.