There are ways to optimize submissions to Reddit/Hacker News for upvotes, yes. (and I've done a lot of research on both services.) However, I would say that neither is rigged; that is, moderators don't control what is seen on the front page. (Although in the case of HN, moderators have bumped up good posts which have not been upvoted, which is a positive intervention)
Product Hunt, as noticed in the article, requires shennanigans to be successful. The real problem here is that PH presents itself as a meritocracy when it really isn't, and it has mislead naive entrepreneurs into thinking a given product is "good" when it truly isn't.
You can only vouch once something has become flagged, but then it works against the flags. (and if only a few users have flagged a post, it is likely to become unflagged by that)
Product Hunt, as noticed in the article, requires shennanigans to be successful. The real problem here is that PH presents itself as a meritocracy when it really isn't, and it has mislead naive entrepreneurs into thinking a given product is "good" when it truly isn't.