I hadn't seen that video stills comparison tool before, very interesting to compare the video quality between cameras. The GX80/85 does seem to be quite soft compared to A6300 at 4K. The 6K to 4K oversampling of the A6300 does really produce some extremely detailed video. For me the GX80/85 is still sharp enough for my needs but if I was someone who makes a lot of architecture or landscape videos the A6300 is a very powerful tool.
EDIT:
I did some more research. The video still of the GX80/85 on the left was taken with the Olympus 45mm at f/5.6 and the video still of the A6300 on the right was taken with the Sony 55mm at f/5.6. I looked up the sharpness fieldmap of both those lenses on DXO at that aperture and there's definitely a difference in sharpness between these lenses at f/5.6. Could this explain the difference in sharpness in 4K from the video stills? Maybe, but I think the A6300 would still be a bit sharper is they both used the same lens (because of the 6K to 4K oversampling) but the difference wouldn't be as noticeable as the example above.