Mobil-1 ATF here also.

With synthetics, it's not just how similar they flow at normal operating temps when compared to regular fluids, it's how well they maintain their viscosities throughout their entire operating range. If you've ever added regular oil to an engine when it's around zero degrees F outside, you've seen how differently it pours when compared to adding it during the summer months. And on the opposite end of the scale, synthetics are designed to also maintain their flow characteristics when hot.

This applies to any full-synthetic fluid though, not just Mobil-1.