I noticed something interesting while seeing how Houndoom did this month when compared to last month. Houndoom usage rose nearly a full percentage point (from 4.74 to 5.68), but it only increased by 1 rank (36 to 35). With such a large usage increase, you'd think 'Doom would have more of a gain.
The reason for this is that UU became much more centralized during the past month. In December, the UU cutoff* was at rank 58, while this month it was at rank 49. Now this is still less centralized than OU, whose cutoff currently stands at rank 44 (so yes, if the tiers were decided using only this month's statistics, Heracross would be in UU). But still, it does make you wonder about PorygonZ and Cresselia.
The reason for this is that UU became much more centralized during the past month. In December, the UU cutoff* was at rank 58, while this month it was at rank 49. Now this is still less centralized than OU, whose cutoff currently stands at rank 44 (so yes, if the tiers were decided using only this month's statistics, Heracross would be in UU). But still, it does make you wonder about PorygonZ and Cresselia.