AFAIR, the full build was also around 30 minutes on a desktop i7. Unfortunately, incremental build (even for the most tiny changes) was around 2-3 minutes which was a real killer for me when I tried to do some open source work on it.
Korean cars manufacturers created now mature brands from scratch. All it took was billions of dollars and a couple decades of time. Can a startup do it? No. Is the market locked up? No as well.