You're correct, this is never going to be fixed by Apple, they just don't seem to care about this problem. I would assume that's because not enough people use FaceTime for the Mac.
I'm of the few people on this thread that seemed to be making progress with Apple. I was in regular communication with a senior tech, who was in communication with the engineers. I sent in several pieces of data from my computer, multiple times, at Apple's request. I thought there was some progress being made at one point, but I have now given up on that idea, and I only use FT on my iPhone and iPad now.
The ONLY immediate solution for this, which I suggested more than once to the senior tech who was working with me, is to simply re-release the beta version of FT for the Mac, which worked perfectly, and did not have this sound issue. I used the FREE beta version for months before I was forced to buy the paid version, since the beta expired. Everyone in this thread who used the beta version also had no problem with it. All Apple has to do is re-release that and problem solved. But for some reason they won't do that.
There is NO solution or fix for this problem. I have tried EVERYTHING more than once. Also, it doesn't matter what machine you're on, or what OS version your running. The fact is, the code in FT for Mac is simply faulty. I was going to use another "F" word, but I chose not to.
I would just suggest that everyone request their $1 back from Apple.