Confusion!!!

https://pokemongo.gamepress.gg/moveset-grades-explanation

They are less likely to survive long enough to pull off a 1 bar charge move on defence so multi bar moves are more preferable, confusion being the optimal defensive quick move.

That is my understanding at least.

They are graded on a curve.

Confusion/Psybeam is a better moveset on defense than Confusion/Shadow Ball, so that shifts the rating that Confusion/Future Sight receives relative to the top moveset.