Where to start???

First it's a single band AP. So it will always take lowest common denominator. You need dual band so that 2.4 devices don't affect your faster N/AC devices. Secondly, 300 is the max speed through the 5ghz radio and that's line-of-sight with you standing next to the device. I'm guessing max 2.4 is 120-150 best case scenario.

Keep in mind, 2.4 signal travels (penetrates) much better than 5. So you aren't likely to cover any large house with 1 5ghz radio.

If you want the output higher, consider using a dual band AP with a 3x3:3 MIMO chain. MIMO helps your overall capacity meaning a 3x3:3 MIMO AP can produce higher speeds than a 2x2:2 AP. Also, test on more than one device. Devices themselves will affect your speed tests along with how many devices are connected wirelessly.