I would say that I'm about slightly above average on hand holding technique. I'm not steady as a rock, but I don't have the shakes either.
I recently shot an event with the 5DSR, here are my thoughts:
The "S" in the 5DS series means studio and they mean it. To get the most out of this camera, you really, truly need to be on a tripod. The same way it is with medium format. To make the most of the resolution, you have to be steady.
I did some hand-held comparisons with the 5DSR vs 6D. The practical results of the 5DSR hand held shots are no better than the 6D. In other words, you just have more resolution to "see" more blur/shake in the pixels when peeping; whereas, lower res cameras like the 6D...this is "masked" in the lower detail. Although, the truth is, even with lower MP cameras, if you properly light the subject and tripod mount the camera - the detail shoots way up....
While the 7D2 and 5DS have the same pixel density, they do not have the same pixel to image proportion. FF vs Crop matters not. The image projected onto the sensor by the lens, there is a different proportion in pixels. This is why the 5DSR show you more of the flaws in technique.
When the 5DS is mounted, it is nothing short of amazing the IQ. No, it isn't medium format. But it is remarkable for 35mm.
Advice:
Keep the 5DS for studio shots and landscape. And other "controlled" environment type shooting. The 5DS cameras are NOT event cameras. You give up FPS, which is more valuable, and gain very little with the resolution considering most if not all shots will be hand held. Only advantage is you can get a nice tight crop with it and have lots of pixels to enlarge IF you were steady enough. But I don't find that too valuable. The ISO is a little weak, but the 5DS has the newer Canon tech that is cleaner.
If you are going to shoot handheld almost all the time, get something else. Any 20-24MP camera is going to be good enough even for studio shots. Put that on a tripod, with good lighting in a controlled environment, and the results are stunning.
As expected, and said in past threads on the subject - the 5DS cameras deliver images of a quality and resolution not useful for anything short of serious landscape or commercial use. Makes no sense to get a 50MP image of something to then provide the client photos they'll view on a 1080 or 4K TV/Monitor (or cell phone), go up on a website, or digital picture frame. Even albums, "regular" 20-24MP cameras can print huge albums at high DPI no problem. So the output, the product of this camera is of no real advantage to those whose end result is low MP, scaled down image.
In short, the 5DS loses its main purpose when handheld - and all you end up with is 2-3x larger image files to deal with in post-processing.