What really annoys me about this line of thought is people treating observations/theories as baseless "fan rules" even if they have actual merit.
It's true that certain arguments, like relevance and the idea that
Those aren't really fan rules. The former was a pretty reasonable observation for the time, especially since they specifically designed a Twilight-Princess style Sheik for Brawl, and they stuck with the TP theme in Smash 4 even after Skyword Sword came out. Even then, "everyone" is a bit of an exaggeration; I recall a lot of people expecting a full BOTW rework for Link. The latter also sounds like a joke.
Honestly, it's annoying to see all of these arguments dismissed as "fan rules." Fan rules usually refer to ideas that limit speculation by creating universal restrictions to potential newcomers ("Third parties can only be from those that have appeared on Nintendo consoles at least once," "Assist trophies can't be ugraded to DLC"), and they have next to no evidence supporting them. The same doesn't really apply to arguments revolving around things like "relevance," which actually does matter, even if it's not to the extent that some people like to claim in order to dismiss certain characters.