I read somewhere that n300 has proprietary mediatek drivers so that it can achieve high speeds. Probably they turned back free driver on latest version. I hope that proprietary will make default on newer versions.
I didnt check this by 3.102 gl firmware, a newer WiFi driver are more sucessfull to reduce the occupancy of channels if no need the traffic. So if you try to compare your maximum traffic speed by your way, it can be you have to look on your way, after 2 or 3 seconds after starting a download of a bigger file.
I have seen on other envirements, WiFi 6 was reducing the channel occupancy much lower if not need for traffic, than your sample are showing. It can be newer driver/firmware are doing this for pre WiWi 6 hardware too.
If you like your get shown a higher speed on the way like you are looking on your speed, you can configure some thing on advanced admin menue:
disable 802.11b, if you dont need
configure youre country ( the defoult is set to us. The us have a lower count of wifi chanels than some other countrys.
configure your chanel use to auto ( that protect your for headache about endless dicussion about possible not ideal channel configuration on your router and around you)
set your chanel bandwitch to the maximum available value on your device like 40, 80 or 160 MHz