The chief difference between here, and Reddit, is that there is no accumulated tally of votes here. Someone can “karma farm” all they want here, and they will have exactly nothing to show for it. Their account doesn’t have a number going up, there is no final score that marks them out as any kind of special.
Adding any kind of system to denote “consistent positive contribution” as you mentioned, or any kind of actually accumulated score, regardless of rolling delay, would only provide incentive for “karma farming” that does not currently exist.
Your proposed solutions would create the problem you’re trying to solve, a problem which does not currently exist.
Disk is for things that are more kiki, but disc, with that rounded off c, is for things that are more bouba.