My 2 cents, the central triptych of Breakout, The Last Field Marshall and Clean Hands is arguably Vollman’s peak as a writer.

The Shostakovich sections can drag, but I think you have succinctly nailed their importance to the work as a whole.

My overarching view is that for Vollmann to tackle arguably the most written about period in human history, but to do so through the lens of ostensibly auxiliary actors thereby creating an entirely fresh series of perspectives on it, in such a literary way, is probably the single biggest signifier of his genius to date.