That's a good point,but the only Pokémon I can think of that the other moves don't hit it hard is actually Rotom,and with a Grass Knot it will make that Volt Switch only a minor scratch.Hell I literally won a final tournament game with a bunch of friends that way,used grass knot ,he used VS didn't do a thing,then used Dark Pulse,flinched him,and Dark Pulse again,and I use Expert Belt,so Greninja can live longer. In my set I don't use U-turn since my Atk IV is garbage,but you get the point,is a good alternative,besides,it one hit KO Tyranitars and M.Blastoises alike,and you don't become Gyarados bait.