Agreed. In the human/AGI case, conditions 1 and 3 seem likely to hold (while I agree human self-report would be a bad way to learn what humans can do reliably, looking at the human track record is a solid way to identify useful classes of tasks at which humans are reasonably competent). I agree 4 more difficult to predict (and has been the subject of much of the discussion thus far), and this particular failure mode of genetically engineering more compliant / willing-to-accept-worse-trade ants/humans updates me towards thinking humans will have few useful services to offer, for the broad definition of humans. The most diligent/compliant/fearful 1% of the population might make good trade partners, but that remains a catastrophic outcome.
I want to focus however a bit more on point 2, which seems less discussed. When trades of the type "Getting out of our houses before we are driven to expend effort killing them" are on the table, some subset of humans (I'd guess 0.1-20% depending on the population) won't just fail to keep the bargain, they'll actively seek to sabotage trade and hurt whoever offered such a trade. Ants don't recognize our property rights (we never 'earned' or traded for them, just claimed already-occupied territory, modified it to our will, and claimed we had the moral authority to exclude them), and it seems entirely possible AGI will claim property rights over large swathes of Earth, from which it may then seek to exclude us.
Even if I could trade with ants because I could communicate well with them, I would not do so if I expected 1% of them would take the offering of trades like "leave or die" as the massive insult it is and thereby dedicate themselves to sabotaging my life (using their bodies to form shapes and images on my floors, chewing at electrical wires, or scattering themselves at low density in my bed to be a constant nuisance being some obvious examples ants with IQ 60 could achieve). Humans would do that, even against a foe they couldn't hope to defeat, so 'keeping bargains' is unlikely to hold, which would make human/AGI trade even less likely.
We can imagine two versions of the mysterious-poverty-restoring-force hypothesis:
Weak: Despite changes in overall productivity, poverty persists.
Strong: Despite changes in overall productivity, the proportion of the population in poverty remains constant.
I think weak is almost certainly true, you're right that UBI won't eliminate poverty. But I think strong is likely false - people desperately struggling: people living relatively comfortably, with slack for hobbies and "fun spending" of time and money doesn't seem constant over history.
I suspect UBI, because the gains are evenly spread (unlike gains from technological development, many of which are disproportionately allocated to the top 10%), would have a pretty sizable impact on the ratio of people living in poverty to people living in comfort.