The quality of a protein is measured using PDCAAS (Protein digestibility corrected amino acid score). It's a score between 0 and 1 that measures the quality of a protein as a function of digestibility and how well it meets the human amino acid requirements.
It is indeed correct that both lentils and chickpeas (which the original comment you replied to was talking about) have a much lower PDCAAS value of around 0.70. Data on beef varies, but it is generally considered to be a complete protein with a PDCAAS score above 0.90.
Instead of accusing "people who insist on eating animals" of lacking scientific knowledge, it would have been much more helpful to point out that the highest quality proteins on the PDCAAS scale are almost universally vegetarian or vegan: eggs, milk, soy, and mycoprotein all have higher scores than beef, chicken, or pork.
The buffoonery continues. These irrational statements are straight out of the meat industry playbook - of course again lacking in any credible citations. And all you had to do was spend even 5 seconds reading a public encyclopedia to avoid this embarassment https://en.wikipedia.org/wiki/Phytoestrogen#Effects_on_human...