Changing the curation/author mix reduces the heavy lifting that downvotes have to do. It takes less downvoting to push self-voting or vote-selling down to 50% than to 25%. There could also likely be more collateral damage with the latter. That said, downvotes alone without changing the split may still work. The question comes down to: 1) degree of relying on altruism since they are still not incentivized, 2) effect of remaining downvote discouragements such as retaliation or social reputation, 3) if the free downvote power is smaller than the upvote power there may not be enough to perform more heavy lifting.
Still, it could work.