I think auto-switching might not be so bad if it works as advertised.
With regards to your static configuration, pulse seems to remember your
preferences pretty well.
I just ran youtube over my headphones and mpv over my speakers. (used
pavucontrol to set it up)
Disconnected the headphones, everything went to speakers.
Reconnected the headphones, only youtube went back to them. mpv stayed on the
speakers as before.
In this scenario, perhaps auto switching would work for you since your
speakers should remain unaffected.
