[hemisphere]

Former ITA engineer here. Our airfare search product QPX was untouchable at the time due to design: it got results that were far better than those of the competitors because ITA was modeling the problem better (search through a graph). While competitor tech debt didn't hurt us, I don't think it was the pivotal factor in ITA's success. As you point out, our hopes of replacing a major carrier's reservation never came to fruition, unfortunately. A res system is a complex beast.

[tyingq]

I do agree that QPX was untouchable, but I still think tech debt in competitors was a major factor. There were plenty of smart people at your competitors...I'm sure graph search occured to them. I suspect efforts to green field that were squashed...nobody wanted to throw out the hairball they had because of the existing investment. Thus, they tried to "fix" what they already had...with obviously bad results.

Edit: And, worth mentioning that your competitors wouldn't have had to be better than, or even as good as QPX. "Good enough" would have squashed several big sales, since shopping was typically bundled in with what their customers already paid.