Play sound from iPhone thru Macbook to external output
Get an inexpensive bluetooth HD receiver and cut out all the middle men and making macos delay the audio is my suggestion. Rogue Amoeba is the only company I know that meets your quality requirements. 


Esinkin Bluetooth Receiver Wireless, NFC-Enabled Audio Adapter 4.0 for HD Home Stereo Music Streaming Sound System for 3.5mm (AUX and RCA) https://www.amazon.com/dp/B07TK8ZKQT/ref=cm_sw_r_cp_tai_xzFIEbX8B4NBV
AirFly Pro is awesome - https://www.twelvesouth.com/products/airfly?variant=30720749109305


There are dozens of great options for less than $25 Cost so all your devices, Mac and iOS can play to your audio system. 

If you must go bluetooth to Mac, try AirFoil - you’re right you don’t need loopback or the full suite and processing. 


https://www.rogueamoeba.com/airfoil/mac/


There are other Wi-Fi / Airplay options for macOS , but AirFoil is what I recommend.