Pluralism rarely announces itself as a religious doctrine the way monism or dualism does, but a great deal of lived polytheism assumes something close to it: many gods, many realms, many kinds of soul or spirit, none straightforwardly reducible to one underlying principle, is itself a metaphysical pluralism about the sacred, even where it is not argued for as philosophy. Animist traditions that treat persons, animals, rivers, and ancestors as different in kind rather than variations on one substance sit closer to Leibniz's picture than to Spinoza's. The tension the position exposes is with any tradition's own theological monism sitting alongside a practically pluralist cosmology, for instance a monotheism that nonetheless populates its cosmos with angels, demons, and souls that behave as distinct kinds of being rather than modes of the one God.
Philosophically, pluralism's chief vulnerability is the same one James accepted rather than solved: a world with no single unifying principle has to explain its evident order and cooperation some other way, whether by Leibniz's pre-established harmony, by natural law, or by leaving the coordination itself as a brute, unexplained fact. Pluralism's sharpest philosophical rival built its case directly on relation: F.H. Bradley's 1893 Appearance and Reality argued that the very concept of a relation between separate things is self-contradictory on close analysis, so that a reality of many independent substances, exactly what pluralism proposes, cannot in the end be coherently maintained.