Mac absolutely can do that, I'm not sure why you think it can't, perhaps it couldn't in the past.
I do it almost daily when I come home and plug in my Bose Companion 5 into my Macbook (USB Speakers)
I do it almost daily when I come home and plug in my Bose Companion 5 into my Macbook (USB Speakers)
It could also have been a borked install as well. But I'm sitting in front of a Win10 install on a Surface 4 Pro, and it can't auto-sink audio.
In fact, I quite often start music playing on the laptop (chrome/Google Play Music) and then power up my bluetooth headset -- it initially uses eSCO when it routes the audio over (mono) and then switches to A2DP a few seconds later
Maybe the issue is something to do with the SW (chrome/firefox?) you use for GVoice? Or maybe there are some edge cases that I'm not triggering (in particular, a USB headset is effectively a new soundcard and not just an audio sink; I can completely believe windows is flaky with them especially with third party drivers)