@geraikenangan,

300 Mbps is the maximum WiFi throughput at 40 MHz channel width. This includes protocol overhead of both, TCP/IP and WiFi layer.

In 802.11n-only mode you can achieve 70% goodput, that's theoretically ~210 Mbps of 300 Mbps WiFi throughput.

Since WiFi is a shared, half-duplex medium, the total goodput is in one direction only (210 Mbps). However, the Ethernet interface is fully duplex and transmits data at 2x 100 Mbps = 200 Mbps throughput, because you can send and receive data at the same time. This matches the WiFi throughput pretty good.

Depending on your region you might even not be able to use 40 MHz channel width if your area is overcrowded in the 2.4 GHz frequency band. With 20 MHz channel width you can expect 144 Mbps wireless throughput, that's roughly 100 Mbps goodput.