Ask Lemmy

I found a reasonably recent (2019) source that splits the difference here, acknowledging that all the amino acids are present in each plant BUT the quantities of some amino acids in any given plant are not high enough to meet human dietary needs.

All plant foods contain all 20 amino acids, including the 9 indispensable amino acids. Importantly, rather than “missing” indispensable amino acids, a more accurate statement would be that the amino acid distribution profile is less optimal in plant foods than in animal foods. Lysine is present in much lower than optimal proportions for human needs in grains, and similarly the sulfur containing amino acids (methionine and cysteine) are proportionally very slightly lower in legumes than would be optimal for human needs. This would be important for someone who ate only rice or only beans, for sustenance, every day.

Dietary Protein and Amino Acids in Vegetarian Diets - A Review

I'd be happy to not cite 'debunked and dated' research, except I can't cite debunking and updated research for the lack of it in my life.