Is any system honestly 100% “securable”? I would argue that any computer, regardless of cpu manufacturer, is “unsecurable”.
https://www.digitaltrends.com/computing/amd-ryzenfall-patch-...
And I believe there's Spectre v2 and/or Meltdown v2 now as well.
You just can't win.
I imagine any computer that approaches maximum security also approaches minimum utility.
Presumably the author just thinks that Intel is a little too low on security compared to the other offerings, and not that the other offerings are actually "secure".
Information can be extracted from airgapped computers by measuring magnetic fluctuations, so this isn't quite true!
Perhaps it is impossible to build a computer without an output mechanism.
Unless you limit your scope to say, Earth, and somehow build a computer outside of Earth's light cone. It is thus causally disconnected from Earth and has no output mechanisms that can be read from anyone on Earth.
But this is more about security engineering philosophy. The Intel management engine relies on a lot of security-by-obscurity, which is not the best way. But I think that Intel chips are passably secure as long as you watch what you're doing.