I don't avoid corn. It is a grain, and currently "out of fashion." Corn allows pellets to be widely available, cheap to produce and thus buy, and are tasty so our birds actually eat them! Corn based "crappy pellets" (as some people will call them) have saved the life of my bird, and have extended the lifespans of countless other birds because of their affordability, availability, and palatability!
I feed fresh corn and corn based pellets and my birds are happy and healthy.
What do the names Harrison's, Roudybush, and Hagen all have in common? They are all pellets with decades of research and a veterinarian behind that research. They also happen to be corn based.
This isn't to say those are the only pellets to trust (I'm currently feeding Zupreem) or that going corn free is bad. I just don't know that it's necessary to avoid corn.