So, this would be my suggestion:
1. Instead of submitting a post, a user can request to get it preemptively approved by mods to prevent it from being flagged
This can take some time, so one downside would be that there would be a delay between the request and the post being visible in the forum
2. If approved, the post stays up no matter what - users can brigade and flag all day long, but the post was already cleared
3. If not approved, the post goes through the normal cycle
Does anyone have a better suggestion to reduce the negative effects of users who misuse the flag/report functionality?
HN is not the whole internet. If you have strong feelings about the current NCAA football rankings, or stupid policies of NYC's Dept. of Homeless Services, or the horrible ethical issues raised by Scorsese's new movie Killers of the Flower Moon - there are a zillion other sites where you can raise and discuss those.
And if the managers or users on those other sites are quick to flag and ban posts about the relative merits of MySQL vs. PostgreSQL, or awesome CSS tricks - that's okay, too.
Instead just internally sticky note people who flag something that is later vouched or vice versa. Then review these noted people and shadow ban their vouch/flag powers if they are making a lot of off decisions.
I reckon an algo like this would catch a person a day and would be easy to review. This reduces trolls.
(BTW: If your submission is fine and gets flagged your other remedy is to submit again a day later.)