I don't really see how that fails to fit the pattern of "I have found that subreddits almost become an anti-expertise forum over time - when actual experts show up to give advice, they are often downvoted if their advice goes against whatever that subreddit is cargo culting (which, as you mentioned, is often not great advice in the first place). Then the expert is discouraged from participating ever again."

While /r/legaladvice is heavily moderated, it is not particularly high quality.