Those would both report "C() takes no parameters" without further enhancements (which would be out of scope for this issue).

The proposed improvement here isn't "Let's make the error message exactly correct in all cases" (that's probably impossible, since we've lost relevant information by the time the argument processing happens).

Instead, it's "let's make the error message more helpful in the most common case for beginners, and let the folks performing the more advanced operation of calling __new__ directly do the translation if they need to"