Karma was useless for that.

Account age helped some.

But, mostly, active moderation is what made spam controlled. You can’t totally do away with bots because the people running them will adapt to anything automated. But a small team of humans (or a single human on a small enough forum) can keep things to the point where any bot posts are taken down before long.

Mind you, reddit automod could help a shit ton. Once you figure out how to set it up, you can fine tune things. Hell, just the ability to make flairs mandatory reduces bots because it isn’t worth the time and effort for the bot runners to set up to auto flair posts. Some will, but not many (and never the usual scam bots, they target subs on reddit with bad moderation to begin with).

You could set up filters to target any spam a given sub would develop by keyword, urls, etc.

So far, lemmy doesn’t need that level of automation, and karma really wouldn’t help things as lemmy exists now. Karma just makes the barrier of entry a tiny bit higher because it’s easy to game.

If lemmy ever does hit hundreds of thousands of active users per hour, automation would be necessary, but the numbers aren’t high enough yet to make it worth the dev focus. And when it does happen, there will probably be user generated solutions anyway.

Right now, we’ve just gotta be willing to report the bots and spammers.