0% effective because there's nothing in Reddit's TOS that says mods have to behave in a fair & transparent manner. That's why there are so many shitty Reddit mods, lol. They can be total unhinged loonies like that mod.

Any mod can ban anyone from their subreddit for any reason they see fit including "disagreeing with your comment" as unfair as it may seem. They can ban their entire community if they want. It would be up to the subreddit's other mods to stop that from happening by revoking mod privileges, reversing bans, etc.

Reddit as the corporate parent isn't going to do anything to intervene in a subreddit unless it's a violation of TOS -- harassment / doxxing, voting manipulation, illegal activity, etc.