Denying that there are substantial differences between animal and plant protein is a weird take. (Anyone with a milk protein allergy is grateful that the proteins in plant milk arent the same as the ones in cow milk) Plant proteins arent always complete and the type of proteins arent the same. Plants for example, dont have proteins like casein which is present in cow milk. And as is pointed out in the linked review, can be deficient in amino acids such as Lysine, Cysteine and Methionine. (The sulfur containing amino acids they refer to) There is also evidence that plant protein by and large isnt absorbed as effectively as animal protein. Which is fine for the vast majority of people. i.e contrary to the fear mongering, vegetarians and vegans still get plenty of protein unless theyve done something horribly wrong. And the lower digestability of plant proteins has been useful in treating proteinuria (excessive protein in the urine) which is usually associated with kidney failure.

The Role of the Anabolic Properties of Plant- versus Animal-Based Protein Sources in Supporting Muscle Mass Maintenance: A Critical Review