I have always been wondering this since people in my area run machamp, can you take out and knockout ERL(an example of a double legend) because there is no statement on the card saying that it is a basic pokemon.
Machamp does not KO Basic Pokémon. Take Out instantly KOs non-evolved Pokémon. There is a difference. While ERL and the other legends like it are not Basic Pokémon, they are also not evolved, meaning Machamp will make quick work of them with Take Out.