Based on the anecdotal evidence of having participated in many such communities, I think reputation systems have a high tendency to create an involuntary “I’m better than you”-effect, similar in nature to the “IT’S OVER 9000!-post count”. Think the /r/thebutton experiment - a self-formed class society of “Greys” and “Reds” - without the “we’ll all laugh about this afterwards” roleplay factor. It’s borderline creepy sometimes, the effect a number (compared constantly to other numbers) can have on someone’s psyche.
Yes, these concepts exist on a forum like Discourse as well; post counts are still there, as are trust levels, but they’re hidden by default. They’re played down, not up, and that makes a big difference. Discourse distinguishes between “Member” and “Regular”, but it doesn’t distinguish between RegularUserX and RegularUserY, which is the point where you may start to value your worth as a community member based on an arbitrary number that’s inflated by behaviour that doesn’t necessarily benefit the community as a whole.