The orchestra certainly was intrusive, better to have just had the section leaders and let them improvise (it is taught in college!) But the composers/arrangers, never mind the orchestra (who probably only had one run through this unfamiliar to them material before the performance)   had worked hard and that deserves some appreciation, even if you (and I) didn't like the result.
Regarding intonation, July Fowlis's singing that normally would be unaccompanied, was certainly different in pitch to when she sang with et instruments, but that is as you would expect. The only serious glitch I heard was the piano, when playing bass to the unthanks, which was quite sharp. Of course pianists no longer tune their own instruments, so the poor bloke was buggered (if indeed he could hear the mistuning- pianists get inured to it). Or the the unthanks could have listened and sung in tune with the bass, even if it didn't fit with their modal/just/other-temperament intonation, like orcheatral musicians do. Do you know how dead a fiddle is when playing in tune with a piano? It's great to get to the bits where the piano shuts up.