Good thoughts here. I too read Hesse back in college in the 70s. "Siddhartha" is a beautiful book, though IMO far from his best.
Hesse's telling of the life of Siddhartha Gautama diverges significantly from the biography commonly accepted in India, though there are some areas of overlap.
It should be understood that there were many buddhas, that title meaning "enlightened one," and Siddhartha Gautama is regarded by most Buddhists as the 4th of 5 universal manifestations of the Buddha in this age.
Westerners in general have tremendous difficulty grasping Eastern religious thought, which has little use for such constructs as god, belief, or heaven.