That's a false dilemma. You don't have to rank comments either chronologically or karmically. You can just look at what the comments say (or go by name, if people made a name for themselves). In other words, have a you-specific karma in your own brain.
I mean what did we expect, it's not so easy to have a ranking of quality.
At least chronological order is objective, karma's reliability is inversely proportional to how busy the idiots are.
You can just look at what the comments say
I don't always have that much time on my hands.
I've gotten sufficient evidence from support that voiceofra has been doing retributive downvoting. I've banned them without prior notice because I'm not giving them more chances to downvote.
I'm thinking of something like not letting anyone give more than 5 downvotes/week for content which is more than a month old. The numbers and the time period are tentative-- this isn't my ideal rule. This is probably technically possible. However, my impression is that highly specific rules like that are an invitation to gaming the rules.
I would rather just make spiteful down-voting impossible (or maybe make it expensive) rather than trying to find out who's doing it. Admittedly, putting up barriers to downvoting for past comments doesn't solve the problem of people who down-vote everything, but at least people who downvote current material are easier to notice.
Any thoughts about technical solutions to excessive down-voting of past material?