You're downplaying "Of course those were interlaced to two sets of 262.5 lines". That is what makes interlaced video 59.94 different images per second, and the difference between 30hz updates and 60hz updates is most definitely noticeable.
The eye's response to changing color is slow, but the response to changing luminance is very fast.
You have expertly summarized the first and last lines of my original post about Color NTSC. Interlacing is effectively dithered color super-resolution at low frame rate with blur from fast motion line tearing at the interlace rate.
Your cones are surprisingly low bandwidth (why old color TVs even worked at
30Hz), while your rods provide danger/flicker cues outside the fovea.
Uncorrelated subpixel scale dithering works just fine at 30Hz.
The eye's response to changing color is slow, but the response to changing luminance is very fast.