Sorry if you felt attacked, it wasn't my point.

Congratulations on developing and shipping a fully-fledged product, I hope I'll help people in need of a "it just works" solution for this particular problem. Paying for it is of course justified, as you poured your time and knowledge to provide a fully working fix.

Since this is Hackernews, I shared how I approached this problem on my devices - I use Hammerspoon to script little parts of the system I don't like in macOS and audio device handling is one of them.

I use a more complex version that handles additional pain points, but the default input source changing has worked just fine for me for the last few years (with AirPods, Bose QC35 and regular wired headphones).