Through your analysis and thoughts, you've come to the conclusion that the term 'high casual' is fluff and you have used logic to explain how meaningless of a term it is.

However, most people have not come to this conclusion.

Ironically, that means it still serves its purpose and therefore has meaning. To put it simply, its like putting the label 'MEDIEVAL FANTASY' on their threads. There are different degrees to fantasy. High fantasy, mild fantasy, steampunk fantasy and so on and so forth. Are you instituting that they need not specify the type of fantasy, that the term medieval is redundant here?

I'm sort of trying to explain that. 'High casual' is simply a tag that OP makes to let people know his expectations. Theres no specific floor for 'high casual' but that doesn't mean its a worthless term.