I don't believe that people's thought processes were more primitive. Their brains were the same as ours are today. They just didn't have the technology to find out the things that we know today.

For example, the ancient Egyptians didn't have access to machines that can measure the electric currents in your brain. They also didn't have the internet with which they could share ideas with people all over the world almost instantaneously.

I do like Plato's idea that dreams express secret wishes. He predates Freud by thousands of years.