I thought you knew and meant that rcon is a protocol, not a software or design style, like nodejs or httplistener.
I thought you meant the only way to send and receive data to a mod was rcon. And once you mention the modding discrod, it is exactly the place I have seen everyone saying the only way to send and receive data from a mod was rcon (the protocol).
Since it is true that you cant open ports or do Internet open operations in a mod for obvious security reasons, that remains the only way natively supported by the devkit to achieve it.