Self sorting directly supports the dynamic I described, because feel-good terrible memes don't fool everyone uniformly. Look at both political herds - each baited with acknowledgement of specific real problems, and then mostly misdirected into avenues that rage against nonsensical bogeymen. It's utterly anti-productive and often self-harming, but it sure makes the participants feel good.
The "elites" want you to move in their preferred direction, yes. But much of that bearing is just common sense - so pushing in the exact opposite direction out of spite puts you further behind and suits them just as well.
If you actually want to actually assert your own independence, you have to do the excruciating work of using reason to figure out the right direction to push that actually represents your own self interest.
You're right. Except that you seem to be implying that the "marketplace of ideas" optimizes for worthwhile ideas, rather than ideas that simply make people feel good - despite being terrible in practice, overly simplistic, fallacious, logically incoherent, etc.
These two qualities used to be in much closer alignment when the Internet was dominated by logical types who would at least try to get to the truth of things, modulo that everpresent lure of feeling superior by knowing something that bucks the common narrative.
But at this point we've devolved to full on Gresham's law as applied to ideas. Anything that carries the slightest bit of nuance or reservation demands analysis (slow path) rather than simple team allegiance (fast path). This is multiplied by the dynamic of sharing things verbatim - either quoted or by reference (URL) - which allows one to effortlessly propagate memes while disclaiming attachment to their own reputation.