I don't understand why you guys keep giving so much oxygen to people who have consistently proven they want to take it for granted and use you for some kind of convoluted soap box (or railroading practice, or *whatever* they get out of it). It's not that I think it's wrong to attempt communication, but doing so with people who have consistently (for years now) demonstrated the same parasitic tendencies - without laying down concrete boundaries - just turns into enabling (which, since I'm not involved, is neither here nor there for me personally except that it junks up the landscape with trolling).
It looks like Jonny was close to successfully doing a boundary thing (asking plainly and directly for very specific support for claims), but he also added a periphery emotional plea that got latched onto and stretched as far as it could. (I assume. I stopped reading. But if the behavior followed the exact same pattern of the past few years, then it's a safe assumption.)
When trying to define gaslighting, it's important to include that the person doing the gaslighting feels a sense of entitlement to overwrite the reality of other people (whether they're aware of it or not , and that they do it - according to Robin Stern, who coined the term for modern psychology use and wrote the first book about it - ultimately because not being perceived by others as always having the right answer is so painful that they have to resort to manipulating other's perception and memory to uphold a status of "being right" in other's eyes). Strong evidence can rightfully "force [people] to question their thoughts, memories, and the events occurring around them," and that in itself is not invariably an unhealthy experience (in fact, the capacity to have that experience with the right evidence can indeed be a mark of emotional/intellectual health). The difference between healthy dialogue and interacting with a gaslighter is that the latter is about power games. I'm not sure how to qualify the character of gaslighting off hand - to effectively separate it from the more honest approach of presenting compelling/pursuasive evidence - except that it often relies on ad hominems and perjoratives instead of clear evidence (e.g. "You're projecting", "TDS", etc).
Stern has said that being gaslighted often has a feeling of 'unreality' accompanying it, and/or has an aftermath of feeling slimed; the consequent feeling of actual healthy dialogue, on the other hand, is very distinct and feels securely like actual growth. (If you're dealing with someone who tells you that the only reason you're not feeling like a conversation is leading securely to actual growth because something is wrong with you: that's a solid red flag you're dealing with a gaslighter).