(1) Put the drive in a USB 3.0 enclosure and perform the same write test. This will use a different driver and a different controller.
(2) If your data are not important, then perform an ATA Secure Erase. This differs from a zero-fill because the procedure is executed internally by the drive, without the need to send any data over the SATA interface. Therefore the drive's write performance will not depend on the motherboard's SATA controller, or anything external to the drive.