What the OP did was "NOT" a controlled test. There are many variables that can cause "movement".
What the OP should had done was to compare 2 cameras and lenses in a studio and shoot against a static subject that does not move. When there's no wind, no vibration of any kind from the floor, table or walls in the studio, then the image from the Olympus would probably be equal to the Sigma. The only concern I have is the Panasonic 12-35 zoom lens. While it's a sharp lens, it's not as perfect as the Sigma 35mm Art lens. But still, the Panasonic can still deliver high resolution images.
Having said that, I've shot with a few hi-res cameras and I find that it presents a very steep learning curve. What happens is that, it works great in a studio controlled environment, but when you take the same camera setup outside and exposed to the elements, everything changes. All the variables that did not move in the studio then moves due to vibration from the ground, wind and atmospheric changes in the environment which then can cause slight motion and reduces the sharpness of the final image. People need to realize that while a high resolution camera can capture more detail from the subject matter, it can also record "MORE MISTAKES" from the lens and the shooting technique.
The higher the resolution the camera can record, the beefier and heavier tripods you must use to get the most out of the camera. But you need to have a controlled result to compare; meaning you need to shoot to make sure your equipment can deliver said resolution output and whatever happened outside while shooting, you need to go through the process of elimination to regain back the loss resolution that can be achieved while shooting in a controlled studio environment. And the most common problem is the tripod and head used.
A friend of mine who is an accomplished fine arts photographer, sells gallery prints just recently upgraded from his Canon 6D to a Canon 5DSR (50MP) and right of the bat, he was facing issues of sharpness. After many trials and tribulation, he had to replace the tripod and head which worked fine with his Canon 6D with a much bigger, heavier tripod and big head to get the sharpness and detail he wanted so his prints would meet the standards of his clients. In that process, he added a few more pounds and would need to carry those pounds up the mountain and on 4 to 7 hrs hike plus his pack. I remembered him telling me that even with all these beefy tripod and shooting at the crack of dawn or dusk to minimize wind, the results are not always perfect.
If you want to find out if your tripod and head is up to snuff for hi-res, then set it up with the said lens and shoot a 5 min video of the subject matter. Jump around the tripod and make movements the same way you would shoot the camera. Then review the video afterwards. If you see little micro jitters, micro movements and shakes in the video, then you know your tripod and head isn't up to snuff. Find the tripod and head combination that reduces the jitters, movement and shakes of the video to the least minimum.
I've played with the Olympus hi-res feature (both E-M5 II/M1 II) and while they can deliver greater resolution for the said capture; upon close inspection I still see some anomalies like double images and cross patterns as opposed to the D810 I compared with. For controlled studio product photography, the Olympus hi-res is perfect for it. But for outdoors, I rather stick with a Nikon, Canon or Sony unless you are willing to carry a much heavier tripod and head to get a good quality shot that can be made with much lighter tripod and head with a Canon, Sony and Nikon hi-res body. There's a lot of movement in the IBIS to create the composite images needed for hi-res and you need a much beefier tripod and head to dampen and arrest the residual movements caused by the environment so as to maintain good manual alignment of the composites.