True about the differences friend. My theory is that Ang Lee played up the differences in the characters because of his ongoing interest in the yin/yang concept of complements.
As far as parallels between the story of Brokeback Mountain and the story of Moses, there are several. While in the desert, Moses saw a burning bush, while Aguirre and Jack referenced a tree struck by lightning that led to the death of 42 sheep. Aguirre is first introduced to us in the story by a description of his desk where there are scribbled-on papers and a Bakelite (A kind of stone) ashtray brimming (brimstone?) with stubs.
Also, when God chose Moses to lead his people out of Egypt, he had Moses practice "transforming his rod into a serpent and inflicting and healing leprosy, and told him that he could also pour river water on dry land to change the water to blood." The leprosy part reminded me of Aguirre's remarks about pneumonia. As for "God had Moses practice transforming his rod into a serpent," no comment!!
Later, Moses got into trouble with God because of a circumcision issue regarding his son. When attempting to get the Pharoah's permission for the Isrealites to leave Egypt, Moses and his brother Aaron caused a plague of frogs to occur. Pharoah insisted he get rid of the frogs, whereupon he made them all die, causing a horrible stench.
Other plagues included gnats and flies, which bothered both Aguirre and Ennis, and diseases to cattle, oxen, goats, sheep, camels, and horses. All of these animals appear in Brokeback Mountain except camels. But wait! Ennis says a coyote is so big it looks like it could eat a camel! Hail and thunder are another of the 10 plagues, and the last one is a lethal epidemic which strikes the first-born male child in each family. Not among the Israelites, though. The plague "pass over" those families, so Uncle Harold did not die after all.
In the end, the Israelites are condemned to wander in the desert until all those who were 20 years old at the beginning of the trip had died. Their children, not them, would be the ones to enter the promised land.