Huh, I didn't even realize that there is no Reddit-like karma system. Well, Lemmy still tracks your total number of posts and comments, so there are those.
Maybe they just want to eliminate having to fetch yet another total, though I see that it does filter by your highest upvotes if you sort by any "Top" category. So someone may end up developing a third-party karma tracker, which may make its way into some Lemmy apps.
Activity is the bottom line for my personal draw to post and comment. I don't care what the vote count is if my submissions are at least being read and replied to; isn't that what matters? If the comments only have the OP's vote, who cares as long as they're insightful? For me, karma is not a measurement of helpfulness, and may in some cases even denote spamminess.
I have no idea of where to find the Lemmy devs' thoughts because general opinion across the fediverse has been training me to avoid Lemmy.ml lol.
Now that I think about it, why don't you use the biography space in your profile for this?
shows people via my profile how much I could help by posting/commenting.