Although Milotic might seem to have a type advantage, against a Pokémon like Aggron, Whimsicott is actually much more proficient.
Against any sluggish Pokémon that doesn't have a type advantage over it, Whimsicott can almost always suppress them effortlessly, without exception—not to mention that Whimsicott's battle tactics are practically one of a kind in this world.
Nobody knows!
Chapter 134