There are four things that matter for transfer speed between storage devices.
How fast the source reads
How fast the target writes
How fast the bits can be moved between them
What post-write nonsense is done.
USB sticks tend to be flash memory with relatively equal read and write speeds, but the spinning disks in a hard disk drive are noticeably unequal. So, unless the USB is very slow, you’d expect a USB to HDD copy to be slower than either USB to USB or HDD to USB.
You can also be slowed down by antivirus scans, on-disk encryption, search indexing, or even the need to move bits from the USB bus to the HDD controller.
There are four things that matter for transfer speed between storage devices.
USB sticks tend to be flash memory with relatively equal read and write speeds, but the spinning disks in a hard disk drive are noticeably unequal. So, unless the USB is very slow, you’d expect a USB to HDD copy to be slower than either USB to USB or HDD to USB.
You can also be slowed down by antivirus scans, on-disk encryption, search indexing, or even the need to move bits from the USB bus to the HDD controller.