JFST doesn’t consider soy milk to be “the best alternative for replacing cow’s milk in [the] human diet” without good reason. As far as nutritious value, soy pretty much reigns supreme when it comes to non-dairy alternatives. First of all, soybeans contain all of the essential amino acids necessary for human nutrition; in other words, it’s a complete protein source, just like animal products are (via PubMed).
In fact, “Only soy milk is comparable in providing with same amount of proteins (8.71 grams) to the human body [as cow’s milk],” according to JFST. In case that’s not enough, soy’s high levels of protein can help lower cholesterol, maintain bone density and decrease fractures in postmenopausal women, and might improve menopausal hot flashes. There’s also speculation that soy’s phytonutrients, or isoflavones, may reduce the risk of cancer, although according to Healthline, the evidence is mixed. In addition to all of that, soy also contains magnesium, fiber, potassium, and some B vitamins.