I think having an opt-in (on by default in Realms) universal bans system is a good idea and something only Microsoft can properly provide. Can you really not turn this off per server?
As far as I know there is no way to disable the reporting, nor is there any way to request a review after you are banned. It is a system set up to enable abuse even more than Youtube's content ID and demonetization bans, and that's saying something.
Spigot/Paper servers can disable chat reporting with plugins, clients can disable sending signatures with forge mods, and servers can be configured to allow clients which don’t sign their messages with the setting enforce-secure-profile.
Already exists for Java edition as a server (Bukkit) mod, which makes it opt-in: https://www.mcbans.com/
Yes - but that doesn't work on Realms and requires the server to trust a 3rd party for the bans list and only works if you use Bukkit. Those problems are solved by Microsoft running the program. But it needs to be optional - ideally opt in. Since Realms is mostly for kids I think it makes sense for this feature to be opt out, or even always on, in Realms.