Hm. I think you're confused about what 'ad hominem' means. That or you're struggling to read more than one sentence at a time as a coherent thought. Do you realize that every sentence past the one with the word 'crackpot' in it was a justification of that statement?
https://en.wikipedia.org/wiki/Ad_hominem says "... is an attack on an argument made by attacking the character, motive, or other attribute of the person making the argument, rather than attacking the argument directly".
So can we agree, at least, that I have attacked the argument directly, at length, and therefore the "rather than..." clause is not satisfied?
Moreover, even if you don't agree with that: I have no obligation not to attack a person directly if it gets the point across faster. I am, after all, writing to the readers as much as gd1 - and if gd1 is truly irrational then I'm not particularly interested in trying to convince them of anything, nor avoiding offending them. And my attack (if you can call it that - I did say "Really hard to not take you for a crackpot", which intentionally gives him a wide benefit of the doubt) was, I think, well-justified:
The definition of the word "crackpot" that I am reaching for is that of "a person who believes absurd notions". That would be as opposed to "a person who believes rationally justifiable notions". I called gd1 a crackpot because as a way of capturing the notion that they were not defending their argument via rationality, but by insistence that it was correct, and were (as I pointed out in my original post) intentionally evading challenges to the argument - but responding to things to that did not challenge it. These to me suggest that they had no ability to defend the argument (and I invited a proper defense), and therefore that they would be a person who believes an argument without rational defense, aka a crackpot.
So I posted the argument that "gd1 is behaving like a crackpot for reasons A, B, C, D", and I listed the reasons. We can substitute the phrase "one who believes absurd notions" for "crackpot". Both the word and its substitution are derogatory terms - we can't get around that. It's a negative quality to believe absurd things.