The right answer is Yes, downvotes will reduce other users pie part
@crokkon wrote a good explanation about it https://steempeak.com/steem/@crokkon/the-steem-downvote-pool-explained
since downvotes reduce the total sum of active rshares, they indirectly increase the payout of all other posts and comments, and this affects authors and curators.
Oh, I have no doubt some sort of redistribution is going on. I'm just not certain that it's quantifiable, so we can say downvotes are actually doing what they're intended to do. There is definitely some reduction of reward allocation going on, along with reallocation of said rewards to others.