as介词短语并非单纯修饰名词,而是与动词focus有关。所以应该剖析为与宾语有关的状语。focus on Aas B 把A当作B而予以关注。
focus either on A or on B as C 要么把A当作C,要么把B当作C而予以关注。
Many theories focus either on the individual or on society as major contributing influence.
= Many theories focus either on the individual as major contributing influence.or on society as major contributing influence.