I just shot a job yesterday with my new XPS 15 (9575), tethered through the USB-C. All I can say is, there IS a difference with the C port. I was shooting RAW+JPEG (50MP RAW, 12MP JPG) and the files flew from the camera and appeared quickly. My assistant/tech even said it seemed much faster than my old computer. (My old computer was a 4-yr old ASUS with a 750GB SSD and USB 3.0 ports.) Could this have been because the SSD in the Dell was faster? Yeah, probably had some impact. I also think part of it is that C1 has improved it's speed. As a comparison, I tried my old standby, EOS Utility/DPP and that combo was slower when previously it had been faster than C1 on my older computer.
In the end, I think there are multiple factors at play (fast CPU, fast SSD NVMe, better performing software), but I think the protocals of USB 3.1 Gen 2 do seem to have some speed benefits for older USB 3.0 devices. Oh, I also have a new Tether Tools cable: USB 3.0 to USB-C. Fatter cable=less resistance?? Native connectors?