RE: HF21 (and 22) are done, how do you feel?
Well, we continue to disagree. I'm aware of the reason for the curve, but I still haven't seen any sort of numbers to evaluate the theory by. I don't know how much of the reward pool was taken by the behaviors CLRC is designed to solve.
That it is a broad brush is the unintended side effect, but, unfortunately, we simply don't know of a better way.
I know it's anathema to this crowd, but KYC would solve this problem. One person, one account would restrict the number of accounts bad actors could have. You could even have a two-tiered system, with opt-in to KYC that gave users access to the linear rewards curve, and opt-out that only gave you access to a curve that had the drawbacks of CLRC without the benefits above that (but the same payouts as linear gave).
Obviously, setting up KYC is a complication in itself, how would the blockchain handle that status switch? Who would be responsible for verifying documents, etc. etc. But it could be done, and if done, it'd be a better way.
Retrospectively is not the point. The point is to build a system that has the greatest likelihood of working going forward. More specifically there was very little need to milk via small accounts previously because milking using the very biggest and accounts, or whatever size happened to be convenient, worked just fine with no downvotes in use practically (<0.1%)!
With enormous costs and requiring an infrastructure that doesn't exist. People already complain about 0.50 worth of Steem paid as a transaction fee to create accounts, which is tiny compared to what any sort of robust KYC costs so, no, I don't think that is feasible.
KYC is not only a matter of being anathema to a crowd but also economics. There is a reason companies like Facebook with nearly unlimited resources (at least compared to Steem!) still have a very high percentage of unverified and fake accounts, and they did even less verification (basically none) when they were trying to grow. It is just too expensive and too big a barrier to growth to do strong verification.
I wouldn't entirely rule it out going forward when the economics make sense but it definitely isn't a solution for Steem at this point.