In the old days, the alternative to store bought baby formula has not been a home-made one, it has rather been a wet nurse. At the time, people had more kids, so there were usually wet nurses available close by.
"Goat's milk contains very little folate and its use as a primary calorie source causes megaloblastic anemia."
Cows milk over 32 oz/day will cause iron deficiency, and "In children this is a hypercoagulable state and can cause cerebral venous sinus thrombosis. I have see this."
Substitutes for human milk designed for human consumption turn out not to be trivial.