MacBook Air Wifi connectivity is not the best among Apple laptops, I have to agree with that, compared to the Pros it’s really sub par. However what you’re experiencing seems to be pointing to a fault of some kind. An upgrade would not be really possible as the only compatible later model is the 2017 Air which has the same specs, but I’d try replacing the Wifi card anyway. Here you can find the replacement board:
[product|IF108-044]
Other than the card, there the antennas in the screen that might get damaged if the Mac was dropped or badly bumped.