Types don't make testing in general unnecessary, but it removes a class of error handling that runtime type checking handles for you. You can really trust the types when using Sorbet.
(I also work in a 40m+ loc non-rails ruby codebase that is almost entirely typed with Sorbet.)
The "closed duplicate" thing is blown away out of proportion than it actually is. I'm convinced people are just pooping on Stack Overflow, not because it's bad, but because they just like complaining about things.
(I also work in a 40m+ loc non-rails ruby codebase that is almost entirely typed with Sorbet.)