Many of the biggest sp holders on Steemit started with nothing. They were made dolphins by whales, in the early months, when there were far less users. Some of them created good content and some of them didn't. Some of them created schemes that purported to support minnows, but they basically embezzled by up voting themselves with the borrowed power. (This was before delegation was implemented.) My point here is that many of them invested less time and effort than people with a fraction of their sp.
Most cryptos are mined by miners who all have the same hash rate (difficulty), but here mining is done by creating content and everyone's hash rate is different. Quality of content is supposed to equal less difficulty, but the social aspect of Steemit means that this is not always the case.
The quality of content only matters in so far that it draws people in, so that the site becomes a social media hub, so the level of shit-posting is actually irrelevant as long as there are sufficient quality posts to draw people in and keep them here. Think about it, FB is a successful site and it's full of people talking crap and posting crap.
The only way to improve Steemit is to increase the number of dolphins so that there is more competition for the established dolphins, in particular the ones who shit-post.