I have been to the pyramids. Many of them are built in a way that makes them pretty funky looking. The 3 at Giza are the biggies that we all pay attention to,but there are some oddly shaped ones that are older. They learned techniques by trial and error, clearly. Stonecutting tools and techniques for masons have not changed a lot. The basic principles are fairly constant. I would say that the manpower has definitely decreased (with the diamond tipped, modern tools, transportation and lifting equipment).
Artisans do things right if they want a particular result. We can see this in centuries old buildings all over the world. And some people just slapped together materials and called it good. Some of those are still around, too. Engineering has come a long ways, but it's math and math is not as hard for everyone as is it to me. Some of the pyramids are pretty badly constructed and show poor engineering. These people were not aliens or geniuses. They were builders.
The pyramids were originally covered with a limestone that covered up the construction details. The way we see them now is probably not nearly as beautiful as they were when they were shiny new, but they are, amazingly, still beautifully majestestic.
If you ever go to visit, take a taxi out, find a guide at the site and you will save a lot over the tour guys from hotels. IF you negotiate with the taxi away from your hotel and IF you negotiate with a guide. Don't ever take the yellow cabs when you are a visitor. Just trust me on this.