Without all the free labor from moderators curating content for topics with different tastes and ideas about what the community should be, it's going to be a struggle to build a community.
Also, I'm mainly on sites like Reddit for the discussion, so those people creating millions of comments in communities are the main draw for me. Finding the perfect karma model was never the solution, we only ever needed one that was "good enough". And that's actually very easy, provided you aren't trying to frankenstein the algo-feed to serve advertisers.