I'm aware - the unfinished obelisk is a prime example.

However, large copper chisels and blades don't account for fine detail carvings or many of the thin bowls and vases made from granite. There are pooling marks and dripping marks on the top of the Serapeum which clearly indicate that some chemical process was involved. Why carve pooling marks into one slab on purpose? Why spend time carving intricate shapes when you can carve the obelisk, then cast the carvings in wax and geopolymer.

I'm saying that a combination of both methods were used. When you know how easy it is to cast something, then quarrying a solid slab stone would have been a huge flex.