Not much. Plenty of nonsense posts/comments are ignored by moderators but the community just downvotes them mostly out of sight. I would say the community itself does most of the work and always has been the case.
Not really. Sort by new and take a look yourself. Nonsense posts get downvoted before a moderator has to do anything. People who sort by top or whatever never see it.
I’ve never understood moderators who are big enough busy bodies to spend their lives removing memes that they dislike so much that they proceed to view every single one submitted to a subreddit so they can remove them.
I moderated a subreddit that went from 50k to 200k subscribers and a lot of automation makes it easier to handle standard spam, but 5-6 mods still spent a few hours every day to make it work. This doesn't show up in any sorting.
I babysit a small sub and have removed around 150 pornbots this month. Maybe I should just leave them since votes are sufficient? It would represent over three quarters of the submissions though.
Posts get filtered by automod rules and anti-spam before they hit the new queue. So this isn’t really sound logic.
The general point you are making IS correct though, upvotes/downvotes are the primary moderation mechanism on Reddit. Moderators are the second layer of moderation, and admins are the third. In my experience the users did an absolute majority of the moderation work except on weird heavily modded communities.
Most large subreddits use AutoModerator and bots that remove posts or filter them for moderator review. Filtered posts are visible to the poster, from the poster's profile, or by moderators. Also, Reddit's spam filter automatically quarantines posts/comments which contain link shorteners and some other sites. None of these systems are apparent to end users unless your post is filtered or removed.
Here are some concrete examples of automatic post removals from my sub.
• Autoplaying Videos - e.g. TikTok
• Short Posts - e.g. discussions under 10 characters in length
• Vague Bodies - e.g. all emojis or punctuation, "lol", "see title", "this", "ty"
• Vague Titles - e.g. all emojis or punctuation, "Looking for...", "THIS", etc.