While it may be true that this particular accident could have been avoided, if both pilots had followed their respective TCAS RAs
Right. This is the reason we're having this discussion. Technically I agree with the "may" bit too as it covers probabilities down to "unlikely, even during the total lifespan of the universe". What Alf & I have been saying is that the aviation industry and regulators, using available data, are satisfied that TCAS provides the best protection in a very short-term conflict,
if the commands are followed.
...the Bashkirian crew's action were rational in light of the perceived three-aircraft-conflict.
Great play is made of the "third aircraft" at Überlingen. After a quick skim through the report and voice transcripts, all I can find in terms of direct evidence is a call from the controller to the Tu-154: "...we have traffic at your... 2 o’clock", whereas radar replays show the traffic to have been at 10 o'clock. The Tu-154 would have been roughly at 2 o'clock, viewed from the 757, so from someone under stress, watching two blips on his radar merging into one, it's understandable that he got it the wrong way round. The report shows that both parties had been seen by each other some time before the collision, so the "third aircraft" conjecture was moot by then.