The Cambridge Dictionary defines:
valency (noun) = a measurement that shows the number of hydrogen atoms that can combine with one atom of a particular chemical element to make a compound, used to describe how easily an element can connect in a chemical way with others.
Of course, that is not the meaning intended, the sentence is definitely not about anything chemistry related.
In this context, "valency" might be understood better as "value" (although it is not a direct meaning in any way):
X has lower value than Y
As though the knowledge gained over centuries of lived experience is of somehow lower value than the literacy acquired in a school.
So the global meaning of the sentence, as I understand it, is:
As if knowledge ... has lower value than literacy ...
Of course, this sentence is just a fragment of a bigger idea. The bigger idea assumes that there were some claims made, and these claims are about "literacy from school" having a greater value than "centuries of experience". And this sentence tries to underline that those claims cannot be true.