I’m not sure, but I think the windows progress bar thingy includes the time spent actually writing to disk, whereas on Linux (or i guess cinnamon) only shows when it gets to disk-cache. If you are full on RAM or tried shutting down immediately afterwards it should take a bit longer since it has to actually write it to disk

Thats my guess anyway

this might not be what you meant, but the word “tar” made me think of tar.gz. Don’t most sites compress the HTTP response body with gzip? What’s to stop you from sending a zip bomb over the network?