This line is basically the review in miniature.

In answering whether Nguyen's argument holds, Runciman decides Nguyen isn't talented enough to be worth judging, then judges him anyway. A book about scoring systems gets scored on the wrong axis. Runciman then uses this to great effect, blending this silly aesthetic complaint with a real structural one.

The structural point I even agree with. You can always take up a new game, but at the social level there is often no other game to play, and you can't opt out of a metric that has power over you. But Runciman doesn't trust the point to carry the piece, so the verdict on Nguyen's prose is enlisted to stand in for a verdict on Nguyen's case.

The irony: to fault the book for not being "compelling reading" is to let a convenient proxy displace the value it was meant to track. That is "value capture" as Nguyen puts it.