Something to consider here; During Era 1 Ruin and Preservation were separate Shards, hence the two metals. Harmony/Discord isn't Ruin and Preservation, he is Harmony/Discord. The two shards have become a single Shard. The scale tipping towards the Discord end would likely effect Harmonium/Ettmetal, but it would change future Ettmetal, not make a second Metal. It is possible if Sazed goes full Discord, then future Harmonium would be "Discordium" instead.
@alder24 explained it well a few seconds before me.
