However the vast majority of times it is used is to refer to a supernatural being or deity
Yes - the vast majority of people also only accept one definition of atheism or God. There are others who are interested in other definitions or fascinated with complexity.
it is a safe assumption to make considering the billions of people who use the word in this context
Most theists don't agree with the definition of God, or a "supernatural being or deity." Ask any two theists, and they will give you completely different ideas or answers. I've tried that experiment and its funny because none of those idiots will agree and it always leads to an argument.
Pantheism is a very different belief compared to mainstream religions
Well, not really - you can believe in all mainstream religions and be a pantheist - and also side with atheists. The only limit is one's understanding of the world.
Pantheism is a very different belief compared to mainstream religions, it is possible to be an atheist and hold those beliefs
Same with any religion.
it is possible (and common) for many Buddhists to also be atheists
Of course - and on a side note - it is also possible for Buddhists to be extremist killers.
This is because the belief does not require acknowledgement of a divine being.
Buddha was considered divine. "I" am considered divine. There are all sorts of ideas that prophets and people have used to tinker with the uplifting idea of divinity.
The reason there is no atheist vs Buddhist arguments is that the two are not incompatible.
I'm not sure if you understand what Buddha expressed.
Atheism and Hinduism, Christianity, or Islam are completely incompatible, as those require the belief and/or worship of one or more supernatural beings.
We've seen throughout history that hinduism and hinduism are not compatible. Christianity and Christianity are not compatible. There are Jews that are killing Jews because they don't accept orthodox beliefs or don't think Israel is an acceptable replacement for Judea as the promised land. Islam is in a modern mess because Saudi Arabian Wahhabism has been protected by Western powers. That Saudi King that just died? Yea, he gave the US cheap oil for decades in exchange that the Western countries never interfere with their insane, beheading, killing other Muslims, dominating woman system. Off topic, but watch this recent BBC documentary about all of that - it starts slow, but it is very eye opening.
That being said, Atheism is necessary for people to stop and think about how they define their surroundings. It is absolutely compatible with everything, and if you personally prefer, nothing.