IIRC there are multiple audio codecs in the standard (and of course different versions of standard), some of them really old. So with certain device combinations you may get better result than with others.

I once looked into these and got the impression that main goal is to make it possible to produce standard compliant devices as cheaply as possible.

Edit: I had written down some of the stuff I found: http://juhap.iki.fi/misc/qc35-windows-bluetooth-audio/