Using the US as an example, too much land is used for cereal grains like corn and wheat, to the point where it has become politically necessary to subsidize worthless and inefficient usages like ethanol just to get rid of the surplus. Ergo, I am making the assertion that if the US can afford to waste arable farmland growing corn that then needs to heavily subsidized to turn into ethanol and HFCS this arable land is being wasted and could be better served as space for solar panels.

Taking land like this out of production will serve the purpose of supporting crop prices (limiting the political fallout of such a move) and it is well-established that modern farm practices have done significant damage to topsoil and that leaving land fallow or planting gaps between panels with prairie grasses will help build back some of the topsoil and soil nutrients.

Do you have a counter-argument to refute my assertion?

Food supply is a strategic priority for any country, and a bit of surplus is to be expected as you want such important things to have a slight slack built into them and not break under stress.

Not everything is done in the name of 110% efficiency.