Overall I think the most important is "B" just like OP stated. At least some semblance of that and in a fashion were there traditional archetypes place in the meta helps punish certain archetypes and thus making way to counters of their own.
To some degree I think we always have a bit of "A" if you go low enough in the rank, as I have taken crappy "fun" decks from some of the most unpopular classes to platinum and diamond in most if not all metas. I do however feel that in the more recent years the powerlevel of the "good" decks have increased so much more making subpar decks that much worse in comparison than earlier metas. However I feel this is natural power creep that is hard to combat without making expansions where a lot of the cards end up being unplayable due to being too low a powerlevel.
The most important aspect to look at to hope to achieve what I feel is a more balanced meta is to make sure most decks have some sort of weakness. Like reducing the resource generation in more tempo oriented decks, try to lower the mana cheat possible for some decks, lower consistency by reducing drawing capabilities. I especially feel like the last year has given some absolutely bonkers drawing capabilities to most of the "top classes".