At the HCI level the Bluetooth protocol is sane enough, it's straightforward to provide a zero-copy interface to the L2CAP layer if you're writing your own host

At the HCI level the Bluetooth protocol is sane enough, it's straightforward to provide a zero-copy interface to the L2CAP layer if you're writing your own host stack. A product I worked on in the past used a serial connection over Bluetooth to Android/iOS apps. In order to communicate to an Apple device, the layers roughly looked like: Radio -> L2CAP -> RFCOMM -> iAP2 The RFCOMM/iAP2 part were redundant. It's understandable that Apple wanted to certify devices, but implementing that as a thin layer over L2CAP and making the profiles on top optional would have made the system much simpler. There may have been historical reliability concerns on the Bluetooth side that justifies what they ended up with, I'm not sure.