UltimoVenusaur
DracoFist FTW
Ubers is the only exception.
BL is double being both a ban list for UU and a place where low usage OU go.
It's not. If Aerodactyl falls into disuse, it will go to UU. If Dragonite does, it goes to BL. Why? Because someone at Smogon will have made a decision to do so based on whatever (base stats, movepool, blahblahblah). BL and 00bers are ban-tiers based on something subjective, not the base objectivity of how much it's used.
I agree with you when you say that maybe the tiers shouldn't be based on usage at all though (it wouldn't really change much, since you can still use everything in OU that isn't an 00ber, and that tier won't change at all if the way tiers are decided is changed).