Soy is a complete protein, meaning it has all essential amino acids. Seitan has 8 out of 9 essential amino acids, is made from wheat and has about the protein density of beef or chicken (~25% according to a quick search).

You get a ton of soy and wheat which would otherwise be feed to animals. Just make tofu and seitan.

However, you're right, you need to supplement some things - at the very least B12. Which a non vegan diet mostly gets from fortified products, meaning its supplemented anyways.