To me the greatest surprise of the whole thread is that Clefable is strangely missing. While I don't think it would make the Top 10 (and I don't think it should tbf) lack of a simple nomination is quite weird (I actually wanted to submit it, but then I forgot to lol). Clef had its fair share of influence on the meta, and it also seems to be kinda resurging atm.
Especially since it kinda ruled the meta for a few months, when everyone ran those WishClef balances with Heatran and the others; when the most OU thing to happen was two Clefable trading rocks/Calm Minding to full and leaving the game at the mercy of crits/PP stalls. It also always had those rarer options like Thunder Wave/Knock Off/Encore, which were often useful to stop other Clefable from boosting (although there were useful for other mons too, obviously). It was often used to stop the broken snake from running through many teams. It also had some influence on teambuilding, especially on stall (stall which lost to CM Clef was simply bad). Unaware Clef have always seen some usage and has been a part of the meta as well.
Now with Zygarde gone, Clef is even more annoying – not only does it have many sets, but also different spreads which let it check mons which it could not before. There is also broken LO variant, not to mention other niche sets like the ladder's favourite Charge Beam + Cosmic Power, which can actually defeat some unprepared teams from team preview. Clef simply should be recognized as an important part of Gen 7 OU metagame.