why is slugging so imbalanced?

Building against slugging as a survivor requires huge opportunity cost, as perks against it are generally single purpose and very situational. Unbreakable, Tenacity, etc. And ostensibly killers mirror that with Deerstalker. But there's not because they have BBQ and Chili, which has no opportunity cost whatsoever as it's immensely rewarding on multiple fronts. I have never once in the past I don't know how many months been in late stages of the game and not seen a slugged survivor used as helpless deadweight against a teammate, because devs have ensured slugging is the only smart thing to do for killers in a 2v1 situation, and ensured that there's no downside to it.

Even if there's a gen close enough to crawl to and hide in the silhouette of, the most a survivor can hope for is a) lie there helplessly while teammate dies b) lie there helplessly as camped bait for teammate or c) IN BEST CASE SCENARIO manage to hide and bleed out unless you've undertaken, again, the opportunity cost of using 1/4 perk slots for something like Adrenaline. Stripping any agency out of a player's hands in late stages of the game and making that the only logical conclusion of play is really dumb game design. ESPECIALLY when it's this one sided and there's no corresponding opportunity cost for the other side.

Some of my favourite matches have been when I died but had a fun, competitive time. Dying isn't the problem. Feeling like a useless deadweight with no meaningful ability to affect the outcome is.

Just today I had someone kill themselves on first hook, a second player hop windows back and forth until killer came and hooked them, then THEY killed themselves on first hook, and then the killer slugged a survivor and stealth camped their body and got almost max BP with final 4k. And that's just the most extreme 'wow that was a mess from start to finish' example, out of many in the past week alone. You've ensured it's a big ol' EZ button.