Kill it by making it suck. Apply rules unfairly and inconsistently, but in a way that affords plausible deniability (ex: over-apply them to controversial posts/comments and let mostly harmless stuff slide if it gets enough upvotes). Slowly trickle in new rules that narrow the focus of the community to exclude content. Lock posts as soon as any arguments start to kill overall discussion. Be a petty tyrant, bait arguments and ban people for arguing back.
Not every strategy may necessarily be applicable to your sub, but I bet a lot could be!
The difference is here you can check the mod log to see what actions have been taken and what reason was given for it, and power tripping admins can’t reach beyond their instance.