I've cropped a section of your comparisons and made one extra one of my own which is using imageoptimise (190KB as was lossless compression) on the original image and scaled that section to 1024px on the long edge, saved them as a lossless tiff and uploaded back to pi.gy which as you said does not compress uploads.

... then I realised that pi.gy must not work properly with tiff's as although it appears to upload them fine, it doesn't give you any links to view the images hahahaha, so I re-exported them as jpeg 100% (i.e. no compression and no loss).

Doing this you can clearly see the differences between the different formats.

- original: http://i.pi.gy/DP55.jpg

- photoshop 60%: http://i.pi.gy/LGmK.jpg

- jpeg.io: http://i.pi.gy/qA3a.jpg

- imageoptimise: http://i.pi.gy/4KOa.jpg

From this, I woud say that while photoshop at 60% (which is very low quality produces a noticeable amount of jpeg compression artifact, it retains image structure and colour depth /significantly/ better than jpeg.io even at such a low quality setting, if you wanted to clean up one an image later, cleaning up the freckled Photoshoppe 60% image would be a lot easier than the very damaged jpeg.io image.

*Edit: Spelling, formatting.