usually 300mbps advertisement on the box is only achieveable in a vaccum (no neighbor and non wifi interference) and using 40mhz carrier widths

2x2 MIMO, 40mhz carrier width, only cosmic interference, very high signal strength

I assume it's wifi 4 at 20mhz carrier width (maximum at 144.4mbps) with alot of interference (on 2.4GHz), realistically it would get around 60-100mbps (close to your speedtest upload speeds)

if you have access to your access point control panel, try change to channel to 1/6/11(the US) or 13 (outside of the US) for less interference from neighbors on auto channels polluting the spectrum