I don't know how much of the reward pool was taken by the behaviors CLRC is designed to solve.
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%)!
but KYC would solve this problem
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.