[conistonwater]

It's worth noting that the consensus in the MathOverflow thread seems to have been that it was a complete waste of time to spend any further time on that paper and the proof. That's the opinion that they reached based on the general issues with the proof itself, and not any promotion committee decisions: specifically the fact that multiple mathematicians tried to read the paper in detail, in seminars, to understand it, and reported that they failed. That would certainly do it!

I don't have an opinion myself on whether it was a mistake to spend more time on it, but you can clearly see professional mathematicians deciding not to work on something "important" for the legitimate reason that they thought it was unsalvageable. If that's correct, then a promotion committee should penalize people for doing it anyway.