> My point is that you can't have corn that is as nitrogen-fixing as a legume and still produce nearly as much corn - the plant (or its microbes) will need the majority of the available photosynthesis products to fix nitrogen. This directly makes the cobs smaller.

I can believe that. However for people who don't want to use nitrogen fertiliser, this might still be useful.

You can see it as an alternative to clover (or manure), that happens to produce eg a bit of grain.