I have 8000 cards running off of sata risers. They work just fine, the problem is people dont understand how electricity works........
This is about safer, not about right or wrong. All of GPUs need to mounted to PCIe 16x that can produce max 75 Watt (on mobo). When we are using "powered riser", we need to make sure that riser will produce the same wattage (max 75 Watt). So we need to make the same condition on it. Since SATA can only produce max 55 Watt (depends on wire rating) and Molex can produce max 75 Watt, so safer using Molex or 6 pins for powering Riser.
I also using SATA connector in a few riser, I think PCIe 1x to USB in riser will produce same as PCIe 1x socket on Mobos (25 Watt max), but I never try to measure it. That's why people said safer using MOLEX or 6 pins than SATA.