I skimmed through the concept; it seems CNN is a direct competitor to Steemit.
I guess more competitors are to arise as MEDIA Protocol would allow anything with a URL to have a large similarity with the functionalities Steemit offers.
But I still believe as an individual platform, Steemit has the advantage. As MEDIA Protocol brings more people into the open content market sphere, a good portion of them are likely to gravitate to Steemit, while continuing to use the platforms decentralized via MEDIA Protocol. It's a win-win with respect to MEDIA Protocol and Steemit.