"third in a series of reviews … a series I am increasingly coming to repent ever having begun."

I think a sample size of three is enough to come to a valid conclusion. I'd never had a high opinion of the Prometheus anyway - what kind of award has such a tiny candidate pool that it has to keep re-nominating the same books over and over anyway? - and I think you've established that the ones on there for their ideological purity are not all that great.