Dismissing the fact that RZA is the showrunner of this series, you DO UNDERSTAND that Wu-Tang and in fact, more than HALF of the Wu-members wouldn't even be rapping had it not been for RZA. He is the one who created WU-TANG and the one that brought them all together. So OF COURSE it will be centered around him mostly, because this is HIS GROUP that HE CREATED. All the other MC's will fall into the fold with the last being Masta Killa because he was the very last to make it into the group and that was well AFTER the group was formed which is still a long ways from now with this series.
As for the significance of Divine. He and Power were the business and muscle behind the scenes. They were instrumental in investing and making deals with labels and booking shows and so forth. They largely handled the business end.
The show is how all of this came together which IS IN LARGE PART dealt with RZA's family because the events that directly happened with him and his family were instrumental to how Wu-Tang was form more than anything.