I feel like if this is your takeaway, you're missing my point on what I think the keystones add? Which is partially my fault for bringing in variety on a single champion to it I guess. The point is more the keystone indicates a play pattern to take note of. I'm saying this primarily from the viewpoint of new players picking the game up and learning now as opposed to earlier seasons. The keystones are a champion agnostic thing for players to look at and relate that to expected gameplay for specific champions they may not know or be familiar with.
That you play differently isn't new; that you can make judgement calls solely off knowing the keystone and use that knowledge of what that keystone means across multiple champions is something fairly new with the keystones being as hefty as they are. The issue of a lack of variety or meaningful options for mages is another thing entirely.
Edit: Basically, I view the keystones as kind of a way for players to take knowledge of one champion / one matchup and better use that information in other matchups. As the champion pool gets larger and larger, this way of reusing things you learn is pretty handy and a nice way to make things not feel ... well, to reuse the meme, as burden of knowledge-y.
