You can create building blocks of unlimited complexity or pure simplicity.

The key lies in your choice of primitives. Do you start off with a set primitives that are extremely complex or a set primitives that are simple but complete in the sense that you can build entities of unlimited complexity by composing simpler primitives?

I would say the latter method is easier. But there's no reason why the former method won't work. Biological evolution has built many examples of working machines with primitives of unimaginable complexity.