The amount of sunlight is not the zero-sum to worry about. For each of us individually the number of hours that we will spend breathing is limited. Life is therefore absolutely zero-sum, no matter what various sophists try to sell.

What they try to sell is how one spends those limited hours, and more specifically - who do we serve in that time. Those few do have the illusion that life is not a zero-sum game. Until death presents them with the winning argument.