Making that measurement per acre makes things look different.
Corn yield of 1 acre =~ 150 bushels
Wheat yield of 1 acre =~ 40 bushels.
So corn is getting subsidized at twice the rate of wheat per acre.
Using your yield figures, priced at today's close on the Chicago Board of Trade, wholly without regard to any subsidy, an acre of soft red winter wheat will gross $211 per acre while an acre of #2 yellow corn will gross $564. It's that corn actually has a value in the marketplace that we plant it.