Sorry if I still don't get it -
You say "1920x1080 1x1 RAW" and "The only downside is the crop factor" - does this mean that the 1920x1080 RAW is still recorded with the Canon FW 3x feature already in the earleir ML vesrions, and then upscaled from 1728x1152 ?
I don't get what you don't get. A "1920x1080 1x1 RAW" is a simple rectangular crop of the center part of the image sensor that has the size of 1920x1080 pixels, meaning that all 2073600 pixels in that area are sampled 1 by 1, as they are - no binning, no line skipping and no upscaling. And this is the cropped image that you get, just in the same way as you would make in Photoshop a 1920x1080 crop of the center part of a still 18 Mp RAW image that you shot with your camera. That's all. In that way you preserve the RAW quality of your cropped image. Cropping means that you do not use the entire sensor area but just a cropped part of it, meaning that you end up with a crop factor. In this particular case, the crop factor is 5208 (the full sensor width of your 18 Mp camera), divided by 1920 (the width of your crop), multiplied by 1,61 (the crop factor of your camera vs. 35 mm full frame camera) which is 4,37. This means that if you use a 10 mm lens with your camera, your field of view will be exactly the same as what you see in the view finder/screen of a full-frame camera with a 43,7 mm lens on it. And that's a downside because you use just a fraction of the sensor area and cannot film wider than that unless you use a fish eye lens.
If you still don't get it, I don't know how to make it clear to you. I am giving up, sorry.