Okay, that makes a little more sense. Let me address this more thoroughly.
The big issue I see with this idea is this: how are you going to determine what is too broken for OUdown? Right now OU and UU are split using usage data because it's the most objective data we can use. However, if we're splitting OU, then we'd likely need another set of criteria. We can use usage data, but what do you make the cut-off point? There are a lot of mons with high usage values that aren't necessarily broken like Garchomp and Clefable. I don't know about you, but I don't see a good cut-off percentage that captures the good mons you want banned without OUup taking a bunch of random non-broken mons with it. You could have a council determine what's broken, but creating tiers based entirely on a council's decision is very subjective and would displease a huge portion of the player base.
There's also the issue of whether it's worth the effort to bother maintaining the tier. The difference between OU and UU (not counting BL mons) is about 50 mons. Just how many mons do you want banned from OUdown? If you ban too many OUdown is UU with a crapton of things they have to ban. Ban too few and you're just playing OU with random mons stripped from the tier. Even if you ban 20, that's a pretty small difference between usage-based tiers considering most tiers ban a little under 60 mons by usage. It's similar to why there's no tier between OU and Ubers: the difference in the tier is so small that there isn't a large enough pool of supporters to merit the extra effort.