That's a pretty broad brush. Check out /r/askscience and /r/askhistorians for some heavily moderated subreddits. Not all need that level but they produce almost all quality posts.
That's the exception that proves the rule. /r/askscience and /r/askhistorians have heavy handed moderation to keep quality much higher than the rest of Reddit.
I don't know how one can disagree with the fact that most of Reddit is quick engagement posts (images, memes, even if they don't fit the subreddit) and witty one liners voted to the top. There's good stuff, sure, the point is that it's hidden behind a ton of crap.
Yeah I'm not sure if there is an "ask" style subreddit for 3D printing, but IME the ask subreddits are a good way to get quality content on a broader academic topic.
There may also be a sidebar on a given sub with more specific related subreddits listed out. These can sometimes be more technical (for example there is a subreddit specific to breaking down NFL plays) or sometimes they are just a way to get a more specific viewpoint (I like to check out both teams' subreddits after some controversy happens, neither side is usually level headed but then you at least get both sides of the story).
I don't know how one can disagree with the fact that most of Reddit is quick engagement posts (images, memes, even if they don't fit the subreddit) and witty one liners voted to the top. There's good stuff, sure, the point is that it's hidden behind a ton of crap.