Are you describing Anthropic?
1. Most people believe in the same one God
2. A lot of the rest are compatible
3. Mistakes are not self-deception
> 2. A lot of the rest are compatible
No one religion covers "most people." You could argue that Christianity and Islam (which add up to ~55%) are the same God because of their Abrahamic roots, but both religions have very important disagreements on the true nature of God that are fundamental to their beliefs and fundamentally incompatible with each other.
Their definitions of God do agree that there is exactly one God... which is fundamentally incompatible with the next two biggest religions (Hinduism and Buddhism) that both hold "there are many gods/divine heavenly beings" as core beliefs.
They explicitly all worship the same God so not "incompatible gods". I did not claim there were no disagreements about the nature of God, but that it only adds one to the GP's claim of 3,000 incompatible Gods. Even if Christians are completely right theologically, Jews and Muslims are still mostly right - one God, a loving creator, omnipotent and omniscient etc.
AFAIK most Hindus are pantheists, so believe on one God, albeit of a very different nature.
Buddhists do not necessarily believe in any god at all.
Buddhism and Hinduism are definitely compatible with each other. I know lots of Buddhists who make offerings in Hindu temples, for example.
Gods of many polytheistic religions are compatible, you just add more gods or identify similar gods with each other (e.g. Sulis Minerva who was also Venus). They can also be compatible with pantheism - you just add more aspects of God.
At the most almost all human religions fit into a handful of broadly similar systems.
One of them (for the most part, at least) explicitly worships one God that exists as three distinct, co-equal divine persons: the Father, the Son, and the Holy Spirit. That view is explicitly rejected by the other two.