Your linked paper doesn't reference mTORC1 a single time. Moreover, the Academy of Nutrition and Dietetics has faced numerous criticisms about it's close ties to corporate groups such as McDonald's, Coca-Cola, Mars, and others.* It is fully within their interest to state "vegans need reliable sources of vitamin B-12, such as fortified foods or supplements" (a direct quote from your linked paper) as it supports the business models of their corporate partners.

*https://en.wikipedia.org/wiki/Academy_of_Nutrition_and_Diete...