If that’s how CAF operate and there’s no contractual mechanism for penalising them, then TfW being disappointed won’t really count for much.
Irrespective of whether that's how CAF operate, surely when contracts were being drawn up, availability of spares and/or availability of the fleet for use should have been considered, with penalties for failing to meet contractual levels.
Another downside of the fragmentation of the railway industry is that each individual TOC probably has relatively little experience of negotiating contracts in the railway industry, or seemingly, a best practice guide to steer them in the right direction (as TOCs and their owners are competing eith one another for contracts).
But it's not as though there was no precedent for including availability of trains for service within contracts. ISTR that some of the contracts with Hitachi specify the daily availability for service of a certain number / proportion of IETs, with payments to Hitachi being reduced if availability falls short.
Hopefully GBR teams will be better able to draw upon and learn from the experiences of previous contractual arrangements, and to ensure that such matters are comprehensively covered, to avoid the issues arising from them. That alone could lead to significant savings for the tax-payer and increased reliability of services for passengers / customers.