If he had said " ...enormous output of art..." without inserting "breathtaking Christian," that might have been an acceptable statement, as long as one included all of Leonardo's drawings and notebook sketches in order to constitute an "enormous" total.
If he had said " ...enormous breathtaking Christian art..." without the "output of" bit, you would certainly be justified to nod your head in agreement while thinking "Yes, Last Supper, of course."
But what we've got is "...Da Vinci's enormous output of breathtaking Christian art ..." and a little problem. Leonardo really didn't paint very many pictures. He's been either credited or associated with less than thirty paintings, which is not an enormous output by anyone's standards. Even Vermeer painted more quickly than this.
To further complicate matters, roughly half of these are secular, not religious in nature. And not all of the paintings in question have been universally accepted by scholars in a position to authenticate them as Leonardo's work. When you get right down to it, there are ten or less paintings by Leonardo that qualify as "breathtaking" and "Christian" - and two (possibly three!) of these are nearly identical canvases.
If you'd care to detour for a few moments, we have a gallery of Leonardo da Vinci paintings arranged chronologically for your viewing enjoyment. Madonna Litta (1490-91), seen here, was among the last works Leonardo painted before embarking on his epic Last Supper project.