Marathon ran 640x480 fullscreen on any 68020+ Mac. It of course ran on the CPU only as 3D GPUs weren't even a thing yet. You are absolutely misremembering these "facts" or just talking out your blowhole.
You see how only a portion of the screen is the actual game environment? Which is exactly what I was describing. You're right, 3D-Specific GPUs weren't a thing, my Radius card was a 7x Quickdraw accelerator primarily, but it is helpful to use the terminology of the current day to connect the metaphor to the current day and example.