For something like a cathedral, having it take a long time is a feature. Of course you could slap something of the same size together from prefab concrete block

For something like a cathedral, having it take a long time is a feature. Of course you could slap something of the same size together from prefab concrete blocks and some 3d printed stuff, but you would "just" get a soulless building with no effort from the faithful invested in it. A real cathedral is a monument for the ages, bigger than any individual who worked on it. Something for entire generations to pour their effort into so that at the end of construction you can say: "my grandfather started building this, my parents worked on it, I worked on it and during the time of my great-grandchildren this building will still be as magnificent as it is now". Trying to build it as quick and cheap as possible is simply not the point for a cathedral.