This is a pretty spare list. I'm diving into this, for no reason.
First off, Batwoman was redheaded for the first season. The actress left and it's a brand new Batwoman who isn't redhaired. That shouldn't be on the list.
Secondly, MJ from the new Spider-Man films isn't Mary Jane Watson and isn't required to have red hair. Also Mary Jane did have red hair in an entire trilogy.
Thirdly... Mera (Aquaman), the Riddler (Batman Forever), Black Widow (8 movies, only 1 blonde), Poison Ivy (Batman & Robin), Jean Grey (6 films, two actors), Mystique (7 films, two actors), Lois Lane (Amy Adams, 3 films and not a redhead in the comics)...etc.
They also cast red-haired actors (like Karen Gillan) for roles where they have no hair or different hair - so red-haired actors are also represented pretty well.
That seems pretty representative for something that is only 1-2% of the U.S. population? If anything, they're over-represented in comics because - shock - it's a more visually-striking color to make your generic citizen alter egos stand out more!