"French, counter-intuitively, is a harder language to sing than German, or that music conservatories simply neglect it." In fact, French *IS* a more difficult language to sing. I would posit there being only 2 French singers in my memory who accomplished any sort of prominent international reputation, and one only achieved fame in recital work, Gerard Souzay. The other, Natalie Desay, is clearly not technically from the French school, wherein the widespread use of nasals has hopelessly blocked the tracheal pipe so that turbulence in the area of phonation leads to early fatigue and short careers, if any.
"---the missed opportunity to stage an historical work."
Come on! Do you say "an horse?" This is a British construction that is occasioned by the dropping of the "h." They would say "an 'istorical..." they might also say "an 'orse."
Blame it on lazy diaphragms.