Frances Moore Lappé.
Just because her protein combining theory ( on the need to combine essential amino acids in the same meal) was wrong and she mostly retracted it, that doesn't affect the complete protein concept's validity.
"Protein combining" theory ≠ "Need to eat all essential amino" acids theory.
Seems to me they are just replacing one myth with an (anti-) myth of their own.
Body cells are made using amino acids, humans can't create the essential amino acids, so they must be eaten from one source or another. Meat - all meat - contains all the essential amino acids in appropriate ratios for the body's needs. Most vegetables do not. These facts don't seem to be disputed.
Those sites claiming that there is a myth surrounding complete protein still accept that you do need all the essential amino acids. They say you can get that from a balanced diet based on vegetables. Can you spot the flaw in that line of reasoning?
Given the choice of eating foods that guarantee all the amino acids I must eat, or a diet that makes it highly likely I get them (if it is varied), I will stick with the guaranteed option.