It's a bit more complex than that in my case. JPG files, lots of them, on a MacBook but the USB drive (having a USB-A interface) is on a Satechi dongle which is plugged into one of my USB-C ports. When I started copying the speeds were nowhere near 480 Mbps, so it would not surprise me if either the dongle is slowing things down, or (more likely) the USB drives are just a lousy quality. I only need to transfer them to my family members, once they've got them they can throw the USB drives in the trash where they belong.
Zipping them into a big archive gets me a file that the drive's file system won't accept, and reformatting the USB drive may throw up other issues. Oh well....