I am confused. He is basically saying Linux isn't powering all the hardware simply because firmware is running on other more complex peripherals/SoCs on a devic

I am confused. He is basically saying Linux isn't powering all the hardware simply because firmware is running on other more complex peripherals/SoCs on a device. That will always become the case as hardware gets more complicated and advanced. Linux simply need to provide the means to abstract the nitty gritty. Linux is still acting as the central "manager" of all the hardware. As far as security. Linux can act as the final security boundary for getting the machine to do anything useful.