You're definitely right about this, the fact that even /r/4chan isn't quarantined despite the content of it's comment section tells you everything you need to know. WPD had very strict rules imposed before the quarantine occurred and the comments weren't nearly as bad as one would expect.
Frankly I think it's obvious that the entire point of quarantines is to hide away the content Reddit doesn't want advertisers to see without any community blowback. Quarantined subreddits are completely ad-free after all.
I remember just last year r/4chan literally had a picture of an overweight woman drinking a big gulp getting fucked doggy style by a man covered in blood with a caption "I have evolved" as the background to their subreddit. 4chan regularly got to the frontpage of reddit and many posts were not marked nsfw. Reddit should have done something about that subreddit years ago, because that could actually turn new users off of reddit.
Frankly I think it's obvious that the entire point of quarantines is to hide away the content Reddit doesn't want advertisers to see without any community blowback. Quarantined subreddits are completely ad-free after all.