Yes this is a very compelling angle for sure. Thanks for the info. It's hard to tell who's to blame. Probably a mix between the 2. Nevertheless, this new machine arrives today and it should statistically run as beautifully as my other iMac once setup.
This will definitely be the last intel Mac I own. They are fantastic machines when dialled in, this is the 1st big issue I've had with any mac I've owned for years, but it does cut deep when you start to realise they do basically just abandon models sooner than you'd think.
Still, I'd take this any day over dealing with a Windows machine and the endless list of pitfalls.
Truth be told, I've actually watercooled these iMacs, which makes them run at full capacity with insane improvements in performance.
Just AIO kits off Amazon modded to run dumb via DC power controllers at a fixed(and silent) speed.
I didn't mention this in the inital comments as i didn't want to blur the diagnosis. But it all runs off its own power supply and doesn't effect anything in the system negatively (tested for EMI, etc)
Anyway that's for another thread with pics I might upload soon.
But this does create a super capable water cooled mac all built into a screen, like they should've done from the get go.
And its through the development of these kits i made where i picked up in the logged analytics, on this mad CPU parasitic effect which seems to be Spectre in some form.
Worth the time and effort when I can get an iMac from 2015 to run as well as a machine 5 years younger and £2000 more, for about £100.
