Revantusk is content. It’s not “systems”, its additional quests and their rewards, and as such is Content, plain and simple.
There might be an argument to made that it is trivial for raiding, and therefore doesn’t change the raiding meta and can be added immediately, but you’re not making that argument. You’re leaning on “Levelling is a system” which is irrelevant to the claim. There is nothing stopping you grinding the shorter patches like we did in 1.1-1.4.