Like your appeals to "common sense" and "no conspiracy would do that" are substantive?
Of course, they are substantive. "Substantive" is not defined by "let's debate CE 399 for the 14,000th time."
"Explain to me how your argument makes any sense whatsoever in the context of a sane, real-world, Presidential assassination" is a substantive challenge because, without a coherent rationale, an argument is simply mental masturbation.
CTers hate these epistemological challenges because, for the most part, they can't articulate a coherent rationale. Whether CE 399 is sufficiently deformed to have done what it is claimed to have done is certainly one issue, but why fabricating and planting it would make any sense at all is a more fundamental issue.
Like you insist that you don't really care that much about the case, but you spend all this time and energy trying to debunk any challenge to the orthodoxy?
Actually, anyone can see that I, in addition to being the Caped Factoid Buster, am actually quite the Fair & Reasonable Provisional Lone Nutter. I am quite willing to be convinced by a plausible, evidence-based conspiracy theory. On the other hand, I spent 40 years poking holes in other peoples' arguments at a professional level and am not going to stop now.
I don't care about the case in the sense of particularly caring Who Dunnit. I'm actually quite sympathetic to Oswald. I'd be happy if he were innocent. I'd be happy, just because it would be fascinating, if there actually was an elaborate conspiracy. But I don't really care. It's just mental exercise in the same way people work crossword puzzles or read murder mysteries and try to figure out Who Dunnit before the end. The fact that even F&RPLNers like myself make so many CTers apoplectic is really quite interesting and suggests that I'm dealing with the functional equivalent of religious zealots (true of many LNers as well, of course).