A very interesting and thoughtful analysis! Here are some counter-thoughts (in no particular order.)

1. Lumping together “Abrahamic” and “Dharmic” traditions is indeed useful for discussing metaphysical and soteriological issues… but it obscures so much in reference to societal impacts. You rightly critique Harris’s over-use of the category of “fundamentalism,” but, I think, fail to note that there is a serious problem with certain brands of fundamentalism. For example, the Spanish Inquisition was a terrible thing and we can all agree that we never hope to see its like revive within a Christian context… but often overlooked is the fact that more people are killed every year in the name of Allah than were killed in the entire centuries-long history of the Inquisition. There is little to compare in the so-called “fundamentalism” of Islam, which is the source of ongoing, empirically verifiable carnage, and that of Protestant Christianity, which is feared by the left mainly because it doesn’t want women to kill their babies in the womb.
2. Which happens to be a situation, if you genuinely think about it from a different point of view, is not so unlike the stand early Christianity took against infanticide, and which they were prone to fixing by rescuing and adopting exposed infants. (Yes, I know I’m raising a hot-button issue, here, but let’s be real, its important.) Note also, that those same Christian fundamentalists are rarely, if ever, given credit for their attempts to provide real and compassionate alternate solutions, like Crisis Pregnancy Centers, which pull tremendous amounts of community resources to help women in crisis with little-to-no judgement, and adoption, which is a compassionate solution that secular progressives seem hell-bent on thwarting at every turn. If you are truly open-minded check out Rosaria Butterfield’s Confessions of an Unlikely Convert. In it she not only gives an interesting alternative take on religion and Christianity (she was a former hard-core feminist progressive herself with a PhD in English focusing on women’s studies and a tenured position at a major university) but also on some of the issues surrounding adoption (she has lived her faith herself by adopting several children herself in spite of the often heart-breaking obstacles put up by our broken system.) Oh, and by the way, fundamentalist Islam does not even ALLOW adoption. Look it up if you don’t believe me. But while Islam sees adoption as a “lie you say with your mouth,” Christianity has built adoption right into the heart of its soteriology, seeing in it a key metaphor for how God treats us and thus how we ought to treat the orphan at our door.
3. ( …controversial discursus over…) Which brings us back to our main topic, that of metaphorical truth…
4. Which is where I genuinely feel like you are determined, Ben, to look at Christianity in only the harshest possible light while looking at any alternative in the rosiest possible light. If you were more genuinely open-minded, you might see more shades in your analysis. For instance, for every “beautiful indigenous spiritual metaphor” Christian missionaries destroyed, they could probably speak of cases of freeing people from unnecessary fear and superstition. And meanwhile, the Dharmic tradition is not without its dark corners as well. At the same time, you seem utterly blinded to the INCREDIBLE amount of damage that has been done to the modern world and to many specific indigenous societies by Marxism, especially under the name of de-colonization. Don’t blame all the ills for the modern world on Christianity while at the same time castigating them for their lack of modernity: Christianity as an idea-system has largely lost control of the levers of power in Western Society today. Keep in mind that Marxism and Nazism are the only two political ideologies that have racked up a body count that can compete with Islam, and they did it in a fraction of the time. What’s more, in our own current situation, by continuing to encourage hatred and division rather than love, co-existence, and attempts at actual solutions, Marxist ideologues have themselves become the leading obstacle to any sort of real progress in our society.