Good points.
My counter would be that Steemit has the potential to be many things to many people and I don't think anyone can accurately predict what trajectory this will take.
I'm still trying to find what works best myself so I'm throwing a number of ideas at the wall and seeing what resonates.
I think the differentiation between Medium and Reddit/Facebook is a good one.
The important question in my mind is 'What amount of posts will yield more value?' and 'Does more posts necessarily mean less quality?"