Sure, maybe my computer might have screamed at me if I tried to watch AV1 or H.265 4K video, but... my computer is 10 years old and so is my monitor, so I don't have a 4K monitor. And, quite frankly, I don't see the point upgrading from 1080 to 4K.
It saves footage in a very inefficient format which is horrible to edit with, so it'll be slow and clunky on anything.
A lot of people editing iPhone footage are going to use a phone-native app like CapCut, but even with that coping with the horribly inefficient compression of h.264 and h.265 footage gets them up to egg-frying temperature very quickly.
Your argument "that's a myth" is based on a task that's so small in terms of percentage it's literally a rounding error.
I'm typing this on a 2010 computer (i7 870 @ 2.93GHz, 16GB RAM), which I also use to write software (C, Lazarus, JS, Go using VSCode, Vim, Emacs), browse web, use web apps (miro, tinkercad, asciiflow, a few others).
Inkscape works acceptably, light image retouching using Gimp works acceptably.
I used to play Starcraft II, Far Cry 3/4/5 on this machine until an upgrade nuked my Wine installation and I didn't bother to fix that.
My steam library is filled with games that work on this machine.
Out of the thousands of tasks that people use their computer for, two of them can't be done acceptably on this machine.
Components using planar transistors will last longer.
This does not help save your electrolytic capacitors, which are a primary limiter of an electronic device's longevity.
I still need to get around to replacing mine with tantalums…
In 2022 a Sandy Bridge (2012) computer is still a viable computer and viable for the foreseeable future. In 2012, a late Pentium III/early Pentium 4 was not yet an antique but already severely outdated.