Sorry to break it to you but Bluetooth also operates on the 2.4GHz ISM band. Those 2.4GHz dongles you're talking about is basically a custom wireless protocol that doesn't follow Bluetooth or any other open standard or OSI stack but is most likely based on some internal protocol of what the three major chip makers in the 2.4GHz space offer (Texas Instruments, Silicon Labs, Nordic Semi) .
I think the world needs less proprietary standards, not more, where the dongle is paired to the device in factory and if you loose the dongle then most likely the headphone or peripheral is instant e-waste.
So I'll stick with Bluetooth for the time being thank you very much.