They don't even bother to use the np.reddit "no participation" domain. Most other subs don't even allow you to link outside the sub, because they've been warned by admins about brigading.
Their rules barely even mention brigading: https://www.reddit.com/r/subredditdrama/wiki/rules, and you have to go to the expanded version of the rules to find even this, which just says not to vote in linked threads.
Literally the entire purpose of this sub is to brigade and harass other subs. Their politics align with those of the admins, though, so it's allowed. It is blatant bullying at the tacit encouragement of the people running the site.
I joined reddit in 2005 and have moderated several subreddits. The admins have never imposed anything resembling that on any subreddit I have moderated. I have a suspicion they impose it when they see a large amount of brigading behavior.
Perhaps it's not applied in an entirely fair or even manner, but I suspect it's only applied when there's an actual problem.
Is simply linking to other threads on reddit sufficient for you to consider something promoting brigading?
As I mentioned previously, linking to other subs, or even simply _talking_ about /r/StarTrek, was enough for admins to accuse /r/Star_Trek of brigading. They threatened to shut them down unless they stopped members from doing that, and so you're not allowed to do it in the sub anymore.
Whether you think that linking to other subs is brigading or not, it's clear that admins call it brigading when they want to shut down subs, yet then let continue on much larger subs dedicated to the act as long as the admins like the sub.
The "good" subreddits will get posters banned left and right, but accounts are cheap and they return.
The "bad" subreddits get banned.
Just mentioning this because I agree with the point you make (in general).
Then there is just arbitrary or malicious enforcement of the rules. /r/Star_Trek was told by admins they would be banned if they talked about /r/StarTrek at all, so now that's a topic that's no longer allowed in that sub. But there are tons of subs set up specifically to talk about other subs, where just about all posts are about other subs (such as /r/subredditdrama), and the admins never bother them.
I don't think we can have a conversation about moderation when people are pretending that the current situation doesn't exist, and that moderation is only ever done for altruistic reasons. It's like talking about police reform but pretending that no police officer has ever done anything wrong and not one of them could ever be part of a problem.