Well, we still won't know who was at fault, because Apple does work around some vendors' issues when it has to.
For example, if Apple found a bug interoperating with Windows PCs, odds are they would have to work around the issue rather than demand Microsoft fix theirs.
Note that Apple can't just "add code" to support the AirPods Pro, but they can use new features in the protocol that weren't used before, and it's possible to even likely that those are what third party devices are choking on.
There is a long legacy of protocols in which certain bits are defined as undefined/for future use but when a device is sent packets in which those bits are now non-zero (or zero) the devices crash and burn rather than ignore those bits as they should.
More to the point I have personally written software that caused various devices to go catatonic when those devices had been shipping into the market for months to years.
In each case I was able to provide the manufacturer with a test case that showed the issue was in their firmware despite, in one case despite having been deployed by the hundreds of thousands on Windows PCs and in various embedded platforms for over a year with zero other complaints.