and I mostly work on my own projects

Then your opinion is absolutely understandable.

It’s also frustrating b/c types don’t guarantee that the system does-the-thing, only that the type-system and compiler are happy, so it’s like pleasing the wrong boss, or some metaphor like that.

Types help you refactoring and communicating with other team members about expected inputs/outputs. Did you ever try debugging a number that should've been a string in a codebase that you didn't write? Example from today: jsforce will throw an exception when you pass a number instead of string due to the fact that the Salesforce server will complain that the type is incorrect. If the method had correct typing of "string", it would save me a few hours of debugging a huge library without visibility inside of it...