I’m a native speaker, and I don’t know the word heel in relation to villains.

Heel is similar to cad, an old fashioned word for a bad person but not necessarily a criminal.

"Heel" is a type of villain, often foolish or comical, but still bad. It is a common term for "villains" in professional wrestling matches.

Heel is a slang term for a bad guy in a storyline. This word is use to describe the bad guy in US professional wresting. If you are familiar with the character Triple H, from the WWE he is considered a heel to some fans.

Perhaps it's not used in the U.S. I haven't heard of it either as a native speaker. But learned something new today!