Welcome to Steemit!

I don't know much about twitter, as I don't use it, but if I remember statistics for Facebook correctly, it seems like they're still growing their active user base with 15-20% each year. So I don't think, at this point at least, that they could be classified as 'dead men walking'. I kinda see it in the same way I see the current crypto currency space, facebook is bitcoin, the reserve, for now the "standard".

That said, I do hope that alternative social media platforms like Steemit or Mastodon can get enough traction and make a good dent in these large corporations profits.