And they should ban throwaway accounts too which you can also see spreading more conjecture.

HN already has a rate limit. You get the message "You're posting too fast" when you exceed it. Though I think it's also tied to karma and might not trigger when all those comments get upvoted. And if you try to downvote them all, you'll run into the protections against mass-downvoting. Tuning the feedback loops to encourage good discussions while damping flamewars is a difficult problem.

Once you have some post history, I’m pretty sure the harsh rate limit, the one that would stop someone from posting in every comment thread, is only triggered manually by the mods if you’re a prick (personal experience).

The basic new account rate limit and the one you get from getting downvote quickly are too weak to stop what they are complaining about.