No, that myth was debunked decades ago. You can get all essential amino acids from a normal variety of plant foods, and the body combines them naturally. Or in case of some all essential amino acids are in the same plant.
All amino acids originate from non-animals (plants, microbes). Where do you think other animals get their essential amino acids? They eat plants or eat an animal that ate plants. All plant proteins have all of the essential amino acids. The only truly “incomplete” protein is gelatin, which is missing the amino acid tryptophan, so the only protein source you couldn’t live on is Jello.
Basically all of your comment is false. Humans can synthesize many amino acids. That is the defining difference between non-essential vs. essential amino acids.
And there are lots of plant sources that are missing or insufficient in essential amino acids. Beans, for example, are lacking in methionine, which is why corn and beans are eaten together in some traditional diets.
Sorry, all essential* amino acids come from plants or microbes. Beans, e.g. pinto, do have methionine, but corn has even less, so I don't see your point.
Besides, you probably don't want a lot of methionine in your diet (it's linked to feeding cancer) [1..7].
Further, you're recycling the tired myth that "protein comibing" is necessary. Our body maintains pools of free amino acids by dumping protein into the digestive tract, which are broken down and reassembled, i.e. it does the protein combining for us, it's not necessary to explicitly do it through meals if you're otherwise eating a varied diet that sufficient in calories.
