Structural static typing lets you do exactly what you claim static type systems are incapable of letting you do. It's fair to say those systems are not common--

Structural static typing lets you do exactly what you claim static type systems are incapable of letting you do. It's fair to say those systems are not common--Typescript is the only one I know of--and I wonder why that is, but it's not an inherent failure of static type systems.