(I'm not a proponent of the 0% corporate tax, fwiw)

If you are running the SaaS from Monaco and only selling things in the US, isn't it right that you'd only pay sales tax?

It's the mismatch when work is done in one place (for some definition of work), but profits taxed elsewhere that's the issue, as I understand it.

0% corporate tax and higher individual income tax works as long as a company and its employees have to use the "full stack" of taxes, and can't mix and match across borders.