Nobody gets to be a purist about this. In toy form, Hello Kitty has been mashed up with the likes of the Justice League and KISS, while the Turtles got spliced with Universal monsters and Star Trek.
Now, if you want to complain that they're less than six inches tall, cost around $73 and are going to be next to impossible to find, be my guest.
Now, when they get around to doing Hello Kitty versions of Freddy, Jason and Leatherface...ehh, you know what? NECA already made these things. Hard to work up much ire either way. No license is sacred.