Yes and it was mentioned but just to reiterate, I also don't think all of the power loss from iron to aluminum block is solely from thermal loss but also to a great extent stability/ring seal. (which they also touched on)

As far as detonation resistance, I think we need to look at it in terms of the title of this thread for starters. The engine masters video was an attempt but I don't think really getting down to where it matters. I think you would need to start with an aluminum headed engine on the edge of pump gas usable then switch to iron to see if it will take the same ignition lead on the same fuel then compare power. At a more realistic/stable coolant temp if we are trying to figure this out for street driven vehicles vs just a drag car. (and I would think that would be the goal)

When they start with an under 10 to 1 engine and high 130's coolant temp and a decent bit of cam, you're miles away from being detonation sensitive no matter what the head is made of.

Yes of course you can transition into detonation instantaneously, I just have a different viewpoint of how heat conduction can affect this, regardless of how fast this can occur.

As a different example, I've calibrated hundreds if not thousands of supercharged GM vehicles with factory piston squirters. Replacement engines that delete these are notably more sensitive to detonation at both part and WOT and do not take as much lead at WOT compared to a stock shortblock. That being said, I don't think the amount of heat squirters could pull out of the piston compares to how much heat a combustion chamber could transfer, especially if we are comparing a material multiples more effective at doing so. (and transferring to a much larger completely surrounded volume of coolant much more efficient itself in heat transfer than oil)

To that example, if the idea that everything is happening too fast for it to matter was true, I don't think you would see much difference with piston squirters, nor do I think manufacturers would bother spending money on them, if they didn't matter.

If you're on board with the idea that when approaching the edge of detonation on a particular combo, that heat can push it either way (safer or over the edge) and also don't dispute Morgan and Meaux's observations on HP output vs material differences, I think it's fair to conclude that if you had an aluminum headed engine on the edge of detonation on a particular fuel that switching to an equally capable iron head may put it over the edge due to it's lesser ability to transfer heat as efficiently.

Otherwise what would account for the power difference?

Just speculation but as far as your observations of never seeing a difference in what engine would take more compression (vs head material), is it possible that like the engine masters comparison, that the engine, whatever it was, was not on the brink of detonation vs the fuel used, with either cylinder head?

Lastly, again, not trying to say there's a miraculous/huge difference, just in cyl head material difference, but I do think it's notable and measurable, for good reason. At least something to be considered, when planning a combination, including vehicle weight, trans type/converter/gearing, intended use (what kind of load it will see)/fuel/etc.