Just because a Pokemon is Fairy/Psychic/etc doesn't mean its good in attacking special-wise. Whimsicott, as evidenced by its Pokedex entries, it preferably rides the wind, since it isn't very strong so it should be quick.
Also shown in the entries, its speed, and its ability, Whimsicott is a prankster. A support role in an RPG. It isn't meant to hit very hard, rather to buff it's own team and cripple the enemy.
Toxicroak on the other hand, fits very well the attacking role. Its best played physically but despite this that doesn't make Toxicroak weak special-wise. It also has moves like mud bomb and sludge bomb, which I assume is deployed from its mouth like in the anime.
Comparing Whimsicott and Toxicroak is like comparing a Healer Sorcerer and a knight who happens to have a laser cannon. Both have different roles, so they have different stats.