iCloud Photo Library takes way less space than library on disk

Thanks for your quick response, I just checked the numbers.

The number shown in the Manage panel is identical to what is shown in the Mac Photos App (both 21,216 Photos and 163 Videos). iCloud.com states the same number of videos and photos.

In the Masters folder within the Photo Library on disk, there are 21,598 files, which is slightly more than the sum of what is shown in the panel. I attribute this to having taken pictures in both RAW and JPG format for a while - I assume that a RAW/JPG pair counts as one photo from the Photos App perspective while consisting of two files on disk.

I have not yet checked if I can download all files from iCloud.com and I'm currently unable to do so because I do not have that much free disk space. ;-)

The creation date of the local master files is the date I restored the library from iCloud. The EXIF information within the files, however, seems to be intact - I checked some of them.

The rough size of the masters on disk matches roughly the size of what I had on disk before switching from Aperture to iCloud Photo Library, so I'd expect the files to have exactly the same content.

Thanks for pointing out that it might be caused by RAW/JPEG pairs. However, are only a couple hundred images out of tens of thousands and would not explain the huge difference. For reference, here is the rough size per extension as used in my Masters folder in MB: