Most Gloranthan religions list hundreds, even thousands of gods. Some of these gods are clearly localized phenomena, deified rulers, or tribal ancestors. Others are alternative titles for gods already worshiped under a different name.
The early Theyalans began the process of identifying and defining the gods, spirits, and powers about them, and establishing unity despite differences of language and culture, however their work was largely confined to Genertela. Similarly in Peloria, the Dara Happans sought to locate any purported deity with the one hundred gods on the God Wall, those deities not identifiable on the wall were false or at least transitory. In the Second Age, the Mythical Synthesis Movement that sought to arrange the gods, spirits, and powers of the world in a coherent and knowable unity.
The God Learners theorized there were approximately two hundred deities of world-wide significance. Not all of these deities had cults. In addition, there were many thousands of minor divine entities of purely localized significance, such as the Racoon Guardians of the Gate of Dusk or the island gods of Vithela. Even the enemies of the God Learners accepted this structure, although they largely accepted those limitations imposed by the Great Mystery itself.
The Lhankor Mhy cult enthusiastically embraced the Mythical Synthesis Movement, and their Knowing Priests played a key role in the later God Learner movements. In the Third Age, Lunar philosophers have added another dozen or so deities (most importantly the Red Goddess and the Seven Mothers), but they too largely adopted the conclusions of the Mythical Synthesis Movement.
This is a really important issue in getting the setting – and something where we need to overcome our modern desacralised biases. We tend to assume that gods are complete cultural constructs – but in Glorantha that is not true. The God Time is real and tangible – our understanding of the gods is of course viewed through the lens of culture (but of course our interaction with the gods also changes and affects our culture), but the Gloranthan gods exist outside of us mortals.