Sure, seitan (aka wheat gluten) is a protein source. How many other grains have a decent protein to carbohydrate ratio though, and are more easily digestible, and don’t cause crippling autoimmune disease or digestive dysfunction in 1-5% of people? You can get concentrated protein from any grain with similar nutritional benefits.

Personally, my sensitivity to gluten has just about ruined my life - right now, my life is on hold and I am staying in a hotel in Rochester while obtaining treatment from the Mayo Clinic’s celiac specialists. Not sure that anyone can say that about quinoa or millet.