Well actually after some testing Ludicolo probably shouldn't be OU, your right Swimming. It just doesn't hit hard enough outside of rain.
(Kind of embarrassing how adamant I was making it OU, oh well live and learn.)
But still, Amoongus should be in OU to counter prominent OU Pokemon, especially the almighty techloom. With spore and regenerator, arguably the best move and best ability in the game, it should be in OU. With sleep mechanics the way they are, a sleeping poke might as well be considered fodder. So Amoongus definitely has its place. And swim your logic behind Amoongus being UU is