I've heard this claim repeated a lot, in the case of soy "very poor" just doesn't seem supported by the data and more importantly in a real world setting one particular protein source lacking a specific amino acid doesn't matter as much because it is mostly not consumed in isolation.

https://pmc.ncbi.nlm.nih.gov/articles/PMC11171741/

But non-animal proteins bio-accumulate less harmfull stuff (like lead) and contain more useful minerals. I hate doing the "the truth is in the middle" guy, but here, the correct diet is clearly in the middle, no?

i agree that plant proteins usually contain more beneficial minerals than meat, but that also certainly includes lead. whole plants and especially plant-based protein products contain lots of lead, but it's unclear if this is a huge problem

https://www.nature.com/articles/s41598-021-91554-z#Sec5 https://www.consumerreports.org/lead/protein-powders-and-sha...

Why does that one particular facet matter the most?

As I understand it diets with modest amounts of animal protein are cheaper, healthier, and ultimately more sustainable for the ecosphere.