According to the Soy bean producers of North Carolina, the soymeal is a by product of the soy oil production, where a small portion is used for Tofu and Soy milk and the majority becomes animal feed: https://ncsoy.org/media-resources/uses-of-soybeans/

So all of the soy protein given to animals would indeed be digestible by humans.

Concerning the corn, we could just plant sweet corn instead, or any other plant really. Or what would prevent us from doing that?