IIUC, what Apple is doing is reducing the number of active channels, so they can keep audio streaming at 48kHz in mono. OP is claiming better audio out quality, which to your point will be unnecessary with the new update, but also better audio in quality by always forcing the external microphone to be the default source, since it's not constrained by the BT bandwidth and is of overall better quality than those of AirPods.

I also think that by doing this, BT audio out can be in stereo/48, which is arguably "better" than mono/48, so their app is still useful.

I personally wouldn't subscribe to it, though. The script OP mentioned on their post seems sufficient for my use case.