You really do like to stretch reality, don't you.
They never said it's the ONLY thing you need to carry, just that you don't need anything else for park entry, FP+, and, if staying at a Disney resort, any POS terminal. They have never said that you don't need ID. They have never said that if you want discounts that you don't have to carry a separate card, like an AP or DVC membership card. They have NEVER stated any such thing. If you don't care about the discounts, or are not eligible for them, then yes, you can visit the parks with nothing more than a driver's license and a MB.