I believe the person you’re responding to is a vegan (from other comments) so the “amino complete” alternative of eggs and dairy you’re suggesting don’t fit the bill of requirements for his arguments either which leaves soy. Mycoprotein has plenty of controversy around it regarding heavy metals and health issues from the fact that it’s highly processed. Soy has a lot of phytoestrogens so it’s not a great candidate to consume large amounts of.