the core "gaming"-problem the PageRank formula has with pages, does not exist with Steem followers: a page can link to itself, and can link to a neighbour same-domain page hundreds of time, thereby "locking up" PageRank inflow. Yet on Steem, an account cannot follow itself, and can only follow another account once

This is also a good counter-argument to the suggestion I keep seeing to also incorporate upvotes along with follows.
A second counter-argument is that incorporating follows makes it many times more operationally expensive.
A third counter-argument would be that votes are much more likely to be bot-driven (a la luckyluke, streemian, voter trails, buildawhale vote clubs, etc.) than actual follows (which in the case of high UA users generally mean they want to see more content from that user, while low UA users may be following follow-back strategies).