No, I'm not saying it's easy, just that doing something very well isn't particularly innovative.
Don't get me wrong, I'm not talking down Medium's product - it's fantastic. But the OP claimed that Medium has "unambiguously, objectively succeeded" in being innovative, and I just don't see it. I'd actually argue that Tumblr was far more innovative - there are some fascinating forms of content that came out of that place, not to mention the whole social network, reblogging effect, etc. etc.
But neither has shaped up to be a particularly successful business, and placing perceived innovation above that might not be wise when you're talking about user generated content. What happens if either of them fails?