Those cheap ones are available in cementious materials, they'd be fine for new build stuff, but that wouldn't fly with historic buildings, where it's often government mandate that things are replaced like for like. I work in conservation, and when we pull a stone, the replacement is often sourced from the same quarry (if possible the same vein) as the original. Mortar matching is also a thing, where a sample is sent into the lab, and the exact same mixture is used, right down to the bits of shell from the same beach if possible.
Also those cheap ones really don't have the lasting power of actual stone.

When you put it that way, I might have to start installing gargoyles on buildings myself.

Imho, do it. We need a little more decorative element in our buildings. Brutalism is not good.

Water jet and a block of stone.

We don't need to make that many gargoyles though. They were mostly installed on high cost architectural buildings, not houses.

I'm any case, it only took this guy 17 seconds to make one from some the old fashioned way:

https://youtube.com/shorts/djbjbFXyN9E?si=NZVpBbJZqrbShXCS