That's short sighted. Buying is beneficial for the price on the short term. As soon as they feel like their group is big enough, that stops and turns. We need growth and a big active userbase, using steem for more than handing out rewards, to become sustainable.
The whitepaper gives guidelines, and colluding groups are mentioned as one of the main forms of abuse. The quality of their posts is irrelevant as long as it is evaluated by their group only and not all of the community. This is how the concept of proof of brain works.
It is about both rewarding quality content and distributing wealth, and there has to be a balance. Downvotes are the tool we have to move some from the latter to the former. The goal is not to get to "only quality", as it shouldn't be "only distribution" either.
The creators we upvote are not randomly chosen, but by a big group of curators. The downvotes similarly are decided on by delegators using their stake to use the function of downvotes as it was intended. Standards on quality and what is overrated obviously differ for everyone, and that's good because it makes the community varied.