You can’t blindly destroy anything in the docs so don’t worry too much about that. All changes need to be reviewed by and accepted by a maintainer including changes to doc. You’d need to create a PR on the openhab/openhab-addons GitHub repo. The docs for each binding comes from that binding’s README.MD file. Clicking on the link at the very bottom of the page in the docs “Edit this page in GitHub” (or something like that) will take you right to the file that needs to be changed.
See How to file an Issue and [Wiki] How to contribute to the openHAB Documentation for lots of details on creating such a PR.
Also take note that MQTT is one of the examples used in the OH 3 Getting Started tutorial. Adding Things - Advanced | openHAB
But it’s also worth noting that how the parts of MQTT “fit together” are not unique to MQTT. The whole bridge Thing with sub-Things that communicate through the bridge is a standard approach for many/most OH 2/3 bindings. So you might consider that if any changes are to be made, they be made in the Concepts section of the main docs and not buried inside the docs for only one binding.