I disagree that it's not framing the discussion. In my questions to the hypothetical polyamorous person, I'm deliberating looking to exacerbate an emotional response. Through the use of words like "devotion" and "cherish," I'm underhandedly implying that there would be a lack of devotion in polyamory. This uses a word which has an emotional connotation in our culture against someone who might be struggling with an idea. So rather than asking the realistic question of whether or not the person would want to spend most of their time with a single person rather than more than one, I've asked them if they fear devoting their time to a person they cherish (thus framing the question into an emotional negative).
I do think your questions chastise on an emotional level whether or not you intended them that way.
"Would you also feel so short-changed if Ginko spent lots of time with a platonic friend and focused lots of attention on him or her?"
The use of "feeling short-changed" implies ownership of a product, that he's not getting his money's worth. Reframing the relationship question in terms of a platonic friend also implies that the situations are similar without demonstrating that they are.
You then frame the entire issue in terms of possession without noting any sort of reality to what would constitute possessiveness versus what wouldn't. You go on to demonstrate how friends might not be inclusive, how he might claim ownership then as well, and how his problem could concern power status.
The problem is you don't really demonstrate any reality for these questions. Your questions and usage of terms are so vague and appeal so much to the emotional responses of a concerned partner that he could easily feel that he was doing those things and just hiding them from himself even if he wasn't.
By not demonstrating a practical reality for what would be a possessive polyamorous person versus a healthy monogamous person in the wrong kind of relationship, you end up showing him a series of emotional negatives that he could identify with without providing viable alternatives.
Additionally, my argument is that the usage of the emotional negatives (particularly with someone in a currently emotionally vulnerable state) do, in fact, frame the discussion. I think the issues and situation could be addressed via the reality of available choices itself without the usage of vague emotional terms (possession, ownership) and slippery slope arguments (framed as questions) utilizing them. That's why I refer to it as chastising. I think the usage (whether deliberate or not) of strong emotional questions with unstated implicit premises clouds the issue rather than helping it.