From what I've seen from experimenting, the only accounts that seem to have weight on each other on lemmy are my lemmy and kbin accounts. There is definitely room for abuse if I were to make many lemmy accounts accross different instances, which I have seen people abuse, especially on lemmy's version of r/place.
I get maybe 2 upvotes at most, and even then I don't usually upvote my own content because it's unsatisfactory. Upvotes tell me people are engaging with my content and like what they see. It does me no good if I know it's just me. The only time I've ever upvoted my own content is on very small communities where no one on would ever see the content otherwise.
I try to be ethical with my interactions with fediverse, but I definitely see the room for abuse.