I suppose in retrospect the great-grandparent could be interpreted as a denial of the latter assumption

It took me a while to realise what you were saying there - I wasn't expecting an indirect insult!

In that case I'm not sure I was clear: the comment could be interpreted as a denial specifically of the "and wouldn't want to send such a signal" part. In other words, it conveyed that you didn't mind being insulting. (Perhaps you consider "I suppose you were willing to be insulting after all" to be itself an insult, in which case the parent is consistent with my having communicated successfully.)

Let's just say we are in complete disagreement about both the subject and about the validity of the arguments used and leave it at that, shall we?

At this point I really don't know exactly what we are in disagreement about, if anything, and more to the point I'm not sure I actually want to know. So "leaving it at that" may indeed be optimal for now.