While I agree with you in general principle, it really depends a lot on how you use your rig.
If you use it in a separate room, sit in the ideal listening spot, use only the highest quality sources and listen carefully and critically to every single track, then yes, there is no point in using bluetooth.
But many use their system in everyday life, in the living room, listening to TV from speakers, watching a youtube video with decent audio, playing background music while chatting or having dinner, for all these things it is infinitely more Convenient to plug in bluetooth and manage everything from your phone.
Better to have one more choice and connection than one less.
Apart from that, frankly, I personally have serious doubts about being able to blindly distinguish an ldac 990 transmission from a bit perfect stream. And I am convinced that very few would succeed, but I could be wrong about this.