According to lalachievements:

53.1% - Pick on Someone Your Own Size I (m4n)
35.0% - Valigarmastered (EX1)
30.9% - Everkept (EX2)
20.1% - Savage Someone Your Own Size I (m4s)

So yes, they are the midcore content. You can safely assume that all the people who cleared m4s also cleared both Extremes for the weapon and accessories, leaving 10-15% of the player base as midcore. Which is quite a good estimate.