This is a really good summary.
It links well with the recent topic on oversized heat loss:
https://community.openenergymonitor.org/t/over-sized-heat-loss-over-estimated-design-temperatures/27795
If we have a truly accurate heat loss and design systems around that then there is very little flexibility for setbacks and heating back up. Most of these discussions centre on the cost/value of electricity as being static. But as we move to a more electric powered society and more renewable generation it seems very unlikely that will be the case.
Your post touches on the fact a night time setback may save power at a time when power is at its cheapest. An alternative would be a setback at peak time (say 4-7pm) when power is at its most expensive, do we need to be designing systems that have the headroom to be able to deliver their heating power is something less than 24h and have the ability to warm back up after a setback (or maybe do half of it beforehand by heating up a bit before the setback).
My anecdotal evidence from living with a system that has a bit more “sensible heat” capacity than your example (say 10kW heat pump for 5kW heat loss) is that the days with the heating switched off at night use less total energy than keeping a steady low and slow. The cost element however is complicated by 1/4 price electricity at night, and a battery which can cover some level of daytime usage. That combination can make the low and slow cheaper, even though it uses more total energy.
I’ve suspected this to be the case but have never seen hard facts about it. Do you have more?? I think many people’s intuition is that running things gently produces the most efficient results, perhaps from our experiences of driving. But in many industrial applications things are designed to be run at full power for extended periods of time.