You could see an HN AMA as one person chiming in on multiple discussions in a short time (which may be much more doable for them), this depends on the questions

You could see an HN AMA as one person chiming in on multiple discussions in a short time (which may be much more doable for them), this depends on the questions asked, of course. And that is something HN hopefully regulates by itself. Just since the 'setup' is the same, it doesn't mean the results will be the same. HN as a whole vs Reddit is proof of this on itself, I would say.