>>57124128I would imagine it was due to different counters and new moves. What's interesting, the most consistent Pokemon over the entire course of the series.
Starmie was OU until Gen 6.
Skarmory was OU until Gen 8.
Tyranitar was OU until Gen 9.
Zapdos has only ever not been OU in Gen 5.
Zapdos and Tyranitar are the peak of combat efficiency. Landorus-Therian will probably be added as well honestly.
