I only scanned the paper, but I didn't see this. Rather, they followed their remit: accepting the government's plans on nuclear as a baseline makes sense as you have to have some baseline, and theirs is not to question what is a largely orthogonal issue.

As to their "total faith in markets", I think it is more a case of assuming the merit order because it is optimal, market or no market. What they are demonstrating is that Hughes' argument amounts to "if you build a large amount of wind power and also behave stupidly, then..."

;-)