A kettle is of course totally a different design, it's just a block of mass not optimizing to dissipate heat at all, or even to keep heat.
If something have heat to dissipate but disspate heat slower than a kettle then it's either design wrongly or intentionally.
That's the idea of the comparision.
And please, when you turn off a camera, CFE not work or should not work. When turn off camera consume very very very low power that you could consider it does not generate heat. If it does, something is wrong here. The comparision with the kettle is just that two heated things got cool down. The R5/R6 need 2 hours, the kettle you could see for yourself. Then you got the idea (in ballpark) how good the thermal design of those cameras is.
And just try to record video while looking thru EVF, you will understand why.
Ok, now I am with you I think....
But we are led to think the R5/R6 have been designed to dissipate heat slowly - whether that is as CanonNews suggested due to an imminent EU law, whether that is because of previous experience with direct sunlight causing problems, or what, we don't know.
Your counter was that the Sigma achieves this in a smaller package without the overheat issues. It can record up to 2h (not sure if that is a battery or card limit or heat), but to UHS II (as SSD although interesting is not so relevant for comparing) it has bitrates up to 1670Mbps which is higher... It is also right on the cusp of what a UHS II can do (210MBps) - based on this link (
https://www.cameramemoryspeed.com/r...eme-pro-300-mbs-uhs-ii-64gb-sdxc-memory-card/)
So whether this means the larger sensor, the CFE, the PCIe chipset, the encoding in the R5 vs the Sigma, the case design or all of the "above" contribute - again, we don't truly know.
Btw, armchair refers to someone who doesnt actually do that activity. Armchair Travellers don't travel, Armchair Landscape Photographers don't actually do landscape photography, and thus an armchair engineer doesn't actually design similar solutions to a camera.
Re CFE - sorry, misled you. I meant the CFE card cools considerably quicker than your kettle when either in camera or outside.
Re 2hrs, yes, I am doing tests which do seem to confirm that. Others have found the time may be significantly less (DPR), which is interesting. Btw, a single source, even one who you consider reliable in my book does not equate to "fact". I need several different sources, we are all human...
And as you are a Z6 / D800 shooter, as I asked earlier "but can I ask, are you even a prospective buyer? If no, then what is the basis for your interest? ". It is a forum, you have as much right as anyone here, but as I wrote to Baron_Karza, "what do you hope to achieve here?"