Interestingly, advertiser, lawyers, and financial traders all have in common that they are agents who play zero-sum or almost zero-sum games on behalf of someone.

Not nearly as much as you think, the game is in a sense locally zero sum, but it greatly benefits the wider system if the right person wins. Hint: consider what would happen if court cases or the resource allocation problems implicit in stock trading were decided by coin flips.

Also contrast with warriors, they really do engage in almost zero-sum games on behalf of someone else, and their game is much less optimized to increase the odds of the right side wining, and yet they're generally considered valiant heroes. The reason being that they were necessary even in the tribal period, so our instincts have evolved to take them into account.