circo
The biggest sub I mod recently grew to ~10k users, it's German speaking, and covers a pretty niche topic. That sub alone is already a surprising amount of work, and 10k is absolutely tiny.
Automod alone removes 4-5 posts a day, and there's still quite a lot of bot generated, irrelevant, or spammy posts and comments that manage to bypass the filters. I can't imagine the amount of spam that would flow in at a subreddit hundreds of times larger than that.
Spez is the perfect example of this. His editing of the comments cemented his reputation as corrupt and stupid, and from then on everything he communicated towards the community received a much stronger backlash than it otherwise would have, regardless of how unpopular the decision actually was.
I mod three small (at most 5k) subs. I'm alone on two of them, and there's two of us for the third one. We've already decided that the subs will be locked and closed once 3rd party apps lose access.