Which Pokémon do you not think are not good enough to be in OU and are only in OU because of their usage stats? My picks are Conkeldurr, Celebi, Jirachi, Mew, Starmie, and maaaaaybe Sylveon. Still undecided.
I don't see how any of those are overrated. Maybe in isolation, but they all have their uses in the right team. Starmie is basically a fast spinner. You can abuse natural cure/recover too on stall teams too.