Or i could just dump a Raspberry Pi Zero W attached to a 10000 mAh power bank in your garden, and wait for it to capture a 4 way handshake. Retrieve the data from the Pi, and throw some serious cloud computing power at it while bruteforcing the password.

Granted, it's going to take longer (perhaps), but chances are you'll never notice until it is too late. Of course, most users won't notice new devices on their Wifi anyway.

People keep forgetting that Wifi is per definition insecure. It's not a point to point technology, and every single packet you send is broadcast in a wide area around you. Furthermore, all current authentication methods, WEP/WPA/WPA2 (excluding WPA3 for now, as it has yet to see wide adoption), have all been cracked in one way or another.