There may not be a lot of superbeings on Earth in the MCU yet, but that's going to change once all the humans with latent Inhuman genes suddenly find themselves with superpowers. It's already started, and I expect between now and Inhumans in 2018 it's going to become a pretty big issue. Once that does happen, the hysteria over mutants in the X-Men universe really won't make much sense if they tried to bring it over to the MCU.
Well, this is assuming the MCU got to have the X-Men in the first place.
They wouldn't need the Inhumans if they had mutants.