Curation rewards depend on what you vote

No, it depends on whether other stake votes for it too, not what it is. It is mostly a measure of concentration.

If I agree to vote after you and you agree to vote after me we both gain curation rewards. Or if we both delegate to a bot and the bot ends up making a single very large vote then we still gain curation rewards. Again, it is all about concentration unless someone else comes along and downvotes. Downvotes are different because they don't directly gain from concentration the superlinearity as curation rewards do. You can't help yourself or agree to help (trade votes with) your friend or swarm together to increase rewards by downvoting (although I guess you could help your friend a tiny bit by downvoting other posts; this obviously is of minimal significance).

Curation is the ultimate 'proof of human' in our network. No bot will ever be able to judge a content better than a human.

That would be ideal, but without humans downvoting where does the input to say whether the curation rewards are being paid to actually 'judge' the content as opposed to just rewarding vote concentration, swarming, vote trading, concentrated stake, etc.?