As a brief update, I rebuilt the driver with debugging enabled and I can verify that diversity is not enabled. I just have no idea yet why. The driver is pretty big and complex and for a bunch of chips. I will need to add debugging code to find the spot where it gets decided that diversity is not going to be used and subsequently find why it is not enabled.
What seems to be pretty clear to me already is that WiFi antenna diversity and Bluetooth coexistence are mutually exclusive. As soon as BT coex is enabled then WiFi diversity gets disabled. This is driver code and I wonder why this is. Other combined modules, e.g. Intel, can do this. But since we do not support Bluetooth right now anyway it is not a real concern.
I’ll keep you posted if I find out more.