Lemmy still relies on upvotes for ranking the feed, so, farming them makes sense, it's just isolated per each post.
And I believe the issue might get worse as Lemmy grows. The reason Reddit came up with karma and all that is because the more people you have on your platform, the more baddies you have to account for.
For now, Lemmy is small enough for a basic interpersonal reputation to mostly just work, but as it grows, we need something else. Presumably, not karma.