Ah, fair enough.
I see Bluetooth headphones as an implicitly mobile option - which assumes:
- Closed headphones only
- A mobile source, likely without a dedicated headphone amp - probably a phone
3, At best a high-quality AAC or MP3 source file; MAYBE FLAC, but unlikely - As you say, some kind of background noise
On that basis, good Bluetooth headphones are as good an option for even the most discerning ear.
Would anyone use a Bluetooth headset in a reference quality audio setup? No, and there’s a reason I use my Senn 650s over my B&W PX when i’m at my desk. But for their context, I would say the PX are as strong an option as any, with the added convenience of wireless and noise cancelling (which very definitely DOES degrade the sound quality, and is a lesson in compromise).
I used to be a gigging musician, and had a pretty good ear myself, but I’ve stood at the front of too many gigs to be reliable these days…