Transfer speed much slower in Wi-Fi than Ethernet I'm transferring a lot of pictures from my Macbook Pro to a local Synology NAS (DS116), using an FTP software named Transmit.
I noticed that the upload speed is quite different between Wi-Fi and Ethernet:

Using Wi-Fi (ac): ~27 MB/s in FTP mode, and ~22 MB/s in AFP mode

Using Ethernet (via a Thunderbolt adapter): ~110 MB/s, in both FTP and AFP modes


I don't understand why the Wi-Fi transfers are so slow compared to Ethernet. Both of them should handle the maximum write speed of the disk (112 MB/s according to Synology).
Any idea about what could be slowing down the transfers when using Wi-Fi?
Notes about my Wi-Fi :

RSSI: -56 dBm
Noise: -95 dBm
TX Rate: 350 Mbps
PHY Mode: 802.11ac
Router: TP-Link AC750
To make it an official answer:

350 Megabit per Second (Mbps) = 43.75 Megabyte per Second (MB/s). Ethernet is always faster and more reliable then Wi-Fi. So when Ethernet is available, use it.