I've been around a lot of social sites too. Several of them have since shut down (Multiply, Orkut, Tsu...). That's a load of data gone forever. At least with a blockchain there's a chance to preserve the data. I don't think there is any 'one size fits all' site'. They all offer something slightly different. What I'd like to see is open standards that allow different sites to work together so we can get the benefit of all of them. I liked Friendfeed (before Facebook shut it down) as that allowed people to follow my updates from various sites without having to join them all.
There's a lot of innovation in social media, but the problem now is that a few players have the public mindshare and it's hard to get people to consider something new. Why should they use anything other than FB when all their friends are there?
I like that Steemit is open source and the data is open. Perhaps it will evolve to allow for privacy when required, but for now it's a cool blogging platform with a lot of potential.