That’s just the state of things. I have experienced this as well, trying to copy a 160 GB usb stick to another one (my old itunes library). Windows manages fine, but neither Linux nor MacOS do it properly. They crawl, and in macos’ case, it gets much slower as time goes by, and I had to stop the transfer. Overall, it’s how these things are implemented. It’s ok for a few gigabytes, but not a good case for many small files (e.g. 3-5 mb each) with many subfolders, and many GBs overall. Seems to me that some cache is overfilling, while windows is more diligent to clear up that cache in time, before things get into a crawl. Just a weak implementation for both Linux and MacOS IMHO, and while I’m a full time Linux user, I’m not afraid to say it how I experienced it under a debian and ubuntu.