Earlier quoted context omitted.
If you have headquarters in California you pay tax here as well as a bit in Delaware The reason to register in Delaware is because of business friendly courts there. I don't believe there is a tax advantage
The federal corporate tax can be up to 35%, which is the highest in the world outside of some literally banana republics. Delaware has a corporate tax rate of 8.7%, California has 8.84. So yes no one is incorporating in Delaware becuase of taxes, WA, TX, NV and a few others have zero corporate tax.
Not sure how state tax rates interact with the federal one though