“I originally had read the entire post, and the “well, duh” still struck me as out of place.”
I disagree. It indicates that the passage is obviously, undeniably true. So much so that if someone didn’t get it, I would want to slap him in the back of the head after saying, “Well, duh.”
I didn’t read the part beginning with “flippant” that way, but if you say that’s what you meant by it, then I have no business telling you what you meant to write.