But the doctrine of advaita vedanta is strictly monist, and thus monotheistic, so that's as far from polytheism as you can get- in a way, the "orthodox" position is monotheism but the "orthoprax" position is polytheism, and it takes a pretty protestant understanding of religion as comprised solely of a set of dogma and beliefs to disregard the way that people actually interact with religion in favour of what the theologians agree they should "believe".
As a Hindu, I get concerned when I see fellow Hindus arguing that their religion fits the definition of monotheism. It seems more like a defense mechanism to competition and denigration by various Christian and Islamic polities rather an integral belief. There is monism and henotheism; but monotheism is certainly not as integral as it to Hinduism as it to these other religions. Hindu thought is quite sophisticated and developed, and is unique in its own right. The Samkhya, Mimamsa, Vedanta, Nyaya, Vaisheshika schools are unique in their own right and have original perspectives therein.
Neoplatonism and maybe Taoism has rather similar monistic beliefs as Vedanta does, but calling it monotheism seems like an attempt to raise their stature to that of Abrahamic religion, as if it possessed some sort of inferior stature in the first place. Just because a religion may not be monotheism does not make its merit any less than a monotheistic one.
Overall, I see a trend where Hindu thought is seen by many in comparison to Abrahamic religions or to Buddhism, rather than on its own merits. That not to mention the "critical" or "psychoanalytic" or marxist perspectives by various "academics" which are of questionable credibility. I see this as more of cheapening of a complex and well developed belief system, if not downright insulting.
I think a good comparison to hinduism are Neoplatonism and Taoism, which possess rather similar monistic beliefs. I see many comparisons of Hinduism to Christianity, Islam, and Buddhism riddled with past connotations of supremacism and inferiority.