Well, to build such a city, you need to find a design for each buildings, some mind-made
and some has been build by using reference pictures. You also need to make the zoning which takes a lot of time (Build roads and such) Plus Lapiz Point, the city in the picture, is all furnished and we built cars by hand and without using WorldEdit. Also, If you ever noticed, each overpasses, roads and buildings & such are perfectly designed like in-real buildings and all at the perfect spot to make the perfect skyline. Our goal is to build the perfect city respecting the in-real city restrictions and to add the most details as we can, signs on stop signs, Car licence plates and more.
So yeah, even if we use WorldEdit, it doesn't mean we are lazy or anything we still build the city and it takes a lot of time to build such a city and also a lot of talent and knowledge.