Bear in mind, it's more complicated than calling a
smeerp a rabbit. We think of them as old-hat, but a lot of very common monster tropes are D&D specific. A kobold might be a creature from mythology, but the tiny dragon-lizard men (or even the yipping dogmen) are a unique expression of D&D.
Of course, video games and such have been aping on D&D's specific expressions for decades now (ever play the original Final Fantasy? Its got more in common Baldur's Gate than FF15), so its really hard to separate what is a unique expression of D&D monsters and what is just public acceptance of said monster. But that's going to be a pitfall for people who leave OGL.