Hinduism is pagan. Pagan is the belief in many gods and in imanent divinity. Hinduism is a vast congeries of pagan systems that added to each other as one group conquered or absorbed another. The spirituality of the Gita is pagan spirituality. It is high order paganism that approaches the atheism og Gautama, but paganism nonetheless and never affected any large part of the population. It could inform the lives of a very few in the ruling class. The lesser folks concentrated on the multiple gods and spirits and worshipped by propitiation of those gods.
If you have studied the Bhagavad Gita, (as I have for more than 30 years) you will see that it is pure monotheism. God is described as the Supreme Person, and all living beings are described as His children.
The monothesm of the Gita is also clearly evident in the Puranas and Upanishads, specifically the Isha Upanishad, among others.
Nou doubt there are many "Hindus" (a culturally designative word invented by the Muslim invaders, describing those who lived on the other side of the Sind River) who haven't a clue about the deep truths of the Vedas, and think that ancestor worship and propiation of demigods is the entirety of the Vedic religion. This is unfortunate.