You might be surprised. I sort of went through a mythology phase so I was probably familiar with the Norse pantheon from other sources. But I also certainly remember watching both that 1960s cartoon (though only remember the theme song) and reading the comics in (mostly) the 60s.

I'd be willing to bet that the majority of Americans who can give a vaguely correct answer to Who is Loki? (or Who is Thor?) know that answer because of Marvel at some point in their lives.