I’d describe the drift towards anti-expertise in terms of size rather than time - I’ve found that the best subreddits are fairly small or have heavy moderation if they are large.

/r/askhistorians has kept up their quality through removing top line answers that are not properly cited, sometimes entire posts have nothing other than [deleted].

I think most smaller communities are still pretty valuable, maybe because they are too small or infrequently used to have their users coalesce around a single set of ideas. I think/r/asknetsec is still a pretty good resource even though it’s in the bigger end of small, I’m not sure how it’s kept it’s quality though.