Flame war detector. If a thread has too many comments (compared with upvotes), it gets downranked

Probably takes into account amount of flags, as well as points:comments ratio.

I have heard that YC alums have more voting power than others.

YC alums have never had more voting power than others. At least I don't remember any time when that was true.

Not true — also, why would YC alums be less likely to upvote a post about Pavel Durov getting arrested?

I heard it directly from a YC alum who said he helped me push a post to the top. But this was several years ago. I didn't mean that YC alums would be less likely to upvote that particular article, but it does make the rankings much more unpredictable.

Another interesting thing is why my post was so heavily downvoted. Did I touch a taboo subject?

It's not taboo—this kind of repetitive meta-discussion is so common that users get tired of it and tend to flag it.