You (and the OP) are echoing Goodhart's Law, which describes one of the reasons that I've lost faith in the wisdom of markets.

yes, however there is an element of real feedback: if an subreddit turns out to be garbage, then people will choose a different subreddit with a different moderation policy. It is possible to prioritize by number of point or by some dynamics over the popularity of an subreddit - that would incorporate this feedback.

I've seen people game bad search engines just the same.