The view of the Cosmos held in Egyptian cosmology is different from that of the Greeks and VERY different from the Norse. The way the Gods are portrayed in the different mythologies is very different and the way these Gods are honored is also different.
Add this element to the differences in modern polytheistic views that range all the way from atheistic to polytheistic (with henotheistic and duo-theistic thrown in) where you have some of the types of Wiccans insisting that ALL Gods are one God with many masks and ALL Goddesses are one Goddess with many masks while other Wiccans only honoring “The Goddess” and omitting the male aspect in worship.
Then you take the differences in ritual format where while Wiccans draw a circle and call the quarters, the Druids don’t and where the Heathens tend (to my knowledge) to have rather informal rituals, Shintos have very formal ones.
Instead of looking at the Pagan and Polytheistic movements as a “big tent”, I propose looking at it rather as a “big campground” with a lot of tents and trails between the tents for people to explore. This analogy admits that the differences DO make a difference while allowing for the free interchange of ideas between the various tents. There would even be the common campfire area — a place where issues could be discussed and rehashed as the Pagan and Polytheistic communities learn to work together for issues that impact us all.