I’ve never had to use the kagi downrank feature. It was the reason I signed up.
I suspect they are aware of their own leaderboards and use those in their ranking algorithm.
Even if they don't explicitly use user blocks to influence overall search ranking, lots of people not clicking on a result because they have it blocked probably does.
Did not expect Pinterest to dominate the “Blocked” dropdown. What does this forgotten site even spam you with? I barely ever hear about them, surprised they even show up in search results.