When bringing my 2013 MacBook Air in my office, not far (but through plaster walls) from a new Airport Extreme router, network connectivity would just go away in a corner, and I chalked it up to "a wifi dead spot." Read your post. Turned off Bluetooth. Greetings from the dead spot—I'm solidly and strongly on the network. Hmmmmmm.

Have you checked your System Preferences/Network settings?

In the main Network Settings window, click the small gear at the bottom of the left sidebar.
Select "Set Service Order".
Arrange your network priority in descending order, Ethernet, Wi-FI, Bluetooth, etc. Click Apply.

Why this works; OS X will check each network for Internet connection according to the "Service Order" setting. If a wireless network is not available, OS X retries for a set period before moving on to the next choice. Moving your primary network to the top means it does not search beyond that.