Should you be punished for something that isn't stated in the rules?

What is actually missing from the rules that you are punished for? If you are talking about a "No no word list" then my answer is yes. Establishing an actual visible list would to people trying to get around by toeing the line to the maximum.

I’m comfortable voting ‘yes’.

Life is full of unwritten, common sense rules. There’s no rule against me calling my boss a %%%%%% to his face, but I shouldn’t be surprised if doing so causes me to lose my job.

I'd need more context to discuss something like this.

Morally I might disagree with it, but legally/technically Riot can do whatever they want because of the TOS we agreed to.

Actually, if you read the rules, they purposefully made parts of it ambiguous and vague, followed by a bit of "will punish you for whatever else they deem inappropriate" which gives them an all encompassing punishment pass within reason.