Public policy, economic activity, lawmaking, are not zero sum. It is the democratic process of taking power that is Zero sum.

If you abstract away from power-taking the policy debate and differences which are such an important part of how these elections are campaigned, then yes, politics is zero sum.

If you abstract away from property-taking the policy differences in running factories, than factories could be stolen or nationalized in a political process with no reduction or increase in national income or production as a result.

Most of us think we know that strong and consistent property law is required to achieve high returns from capital, i.e., that the way capital is deployed and factories are run is NOT divorced from how the ownership of factories is determined. Most of us think we know that strong and consistent laws protecting a significant portion of return on investment is required to get the most out of factories.

Is there any reason to think it makes more sense to divorce policy differences from the aspect of politics which is zero-sum than it does to divorce how a factory is run from the methods under which its ownership is determined? That is, is a model that treats politics as zero-sum too falwed to use for much?