As you wrote, there’s regularly some debate. That’s why it’s also useful to have an authoritative source of truth to confirm what a server should do if we want to make it follow the standards.

And that’s where RFC 7231 (section 4.3.4) comes in to confirm what you wrote:

If the target resource does not have a current representation and the PUT successfully creates one, then the origin server MUST inform the user agent by sending a 201 (Created) response. If the target resource does have a current representation and that representation is successfully modified in accordance with the state of the enclosed representation, then the origin server MUST send either a 200 (OK) or a 204 (No Content) response to indicate successful completion of the request.

src: tools.ietf.org/html/rfc7231

Every time such discussion starts in a design doc review or code review, following RFC is very helpful. We need very strong reason and special edge cases to pick non standard behaviors.