Keep in mind WiFi is half duplex as well.
I read your reply twice and can't tell if you tried what I suggested. 802.11n 300 Mb speed is only in theory and includes but up and down bits during testing which you find most apps never include both in the speed test.
In fact I have set some WiFi networks all the way back to 802.11g and found better performance from that. That's still 54 Mbps and more than what you are getting.
There's a lot to cover here. WiFi is a SHARED access system so you rarely see any client hit the max. Your posts seem to tell me this is one of your first forays into this networking.