The term "Great Spirit" is not as cut and dried as you make it out to be and in many, if not most cases absolutely describes a non-anthropomorphic force of nature. There was a huge diverse set of views which spans the spectrum of monotheistic, polytheistic, pantheistic, and combinations of two or all of these things at different times.
Possibly the biggest examples are the Lakota and Algonquian tribes who at times subscribed to a spirit force found in all things. As is the case with most indigenous tribes that lacked writing, oral history changed the nature of their beliefs over time.
Just because a religion incorporates mythology, doesn't make the religion deistic. Many Native American tribes knew there myths were just that. They were used as teaching tools to describe their views of spiritual forces which they well understood were incomprehensible.
Buddhism most certainly includes non-deistic beliefs. Although gods were believed to exists, they were viewed as non-omnipotent. Religion includes philosophy by most definitions. It's not really a case of them being more like a philosophy, they all are a philosophy.
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