I think the basic thing here is that you seem to want to judge the "health" of the metagame somehow, and I feel that doing so is not useful. Is vintage healthy? I think so, and the fact that I can't play Nimble Mongoose in my deck doesn't take away from that for me. Essentially, I feel that you are imposing yourself and your ideas about what a "healthy" metagame is on the format, and I think that is presumptuous and meaningless.