The problem is even that is more nuanced than what we get from father and son.
Again, my issue is not that the father takes a pessimistic view of history, and the son takes an optimistic view. It's that they take their respective views because that's what they want to convey to people now, rather than what they actually think happened.
Reading the justifications from both father and son (the father more so), they're both trying to present an interpretation of history that is intended to push their own broader philosophies. Taking the Viis encounter stela as an example, the father says that he prefers the interpretation that the Viis and Qitari had a bad first meeting, because that would make their current good relations "more meaningful". Not because some small detail in the discovered stela implied that interpretation, or he had corroborating evidence; just that his reading would fit his worldview better.