Very good points and good critical thinking. However it's important to note that platforms such as reddit and facebook are the ones getting paid to advertise. Essentially offering a 'free' service and in turn being allowed to use their users as products for data mining/advertising ect. Steem removes the middle man, facebook and makes the users shareholders of the system. Thus allowing for users to 'sell' themselves to advertisers/marketers directly instead of facebook doing it for them.
Whether this type of free market content will become stale or hijacked by marketers will be decided by the user base itself, since they have voting rights on what content appears. There should also be incentive for users/whales to promote content that attracts more people to the system, thus giving it more value.
I predict this idea of selling yourself & your effort will inflate the value further before people drift away from the platform for the amount of spam, then stabilising & increasing slowly and the core community around here starts to develop.
Look at me... I'm just posting for upvotes and access to the coin speculatively, so most posts, upvotes & comments will be hysterical & low quality for a while. Growth will be much more akin to the growth of other social networks. Steemit.com doesn't have much on-boarding advantage over incumbent social networks, it just seems to be a better long term model, a more morally acceptable economic model, but that only points to slow sustained growth, not immediate exponential growth.