Those numbers look to be in a system with some other overhead/driver issues. My lower-interrupt PC did over "400MP/s" on an i7-3770 running at 8% average CPU utilization. My i7-4770 system consumes more CPU time due to some system overhead someplace, which I've quit caring about since I couldn't pinpoint the issue.Take a look a this test. Running 9 Dahua 4MP cameras at 30fps with live view at 30FPS. Max observed CPU usage for 3 seconds on task manager with nothing else running on the Win10 6700K computer. Further testing needs to be done at lower live view FPS since there is a dramatic reduction in CPU with lower FPS. Maybe later when I have time i can repeat the test at 15 FPS live view.
That was down from something like 70% CPU without Quicksync iirc. Pretty much maxed out at 70% on an i7, since hyperthreading is useless. So if we assuming going from 100% on 4 physical cores, down to 16% (8% overall thread utilization), that's an 84% reduction in CPU needs. Much better than your figures.
Quicksync is strongly recommended, but the Ryzen CPUs show promise. An i7 still jumps in power usage pretty quickly (one core in turbo/12% total CPU on an i7 will make the entire system start pulling upwards of 70W. A more power-optimized PC could likely handle the same load at under 30W, but it needs to be built for that. Same way my i7 Thinkpad can consume as little as 6 Watts and peak around 30, whereas other laptops idle at 15-20. CPU is only one part of the puzzle - the entire platform means a lot.
My i7-4770 is still taking around twice the CPU time as the i7-3770 system used, but even that system is still a drop of around 70% from non-hardware-accelerated.