Even after that, the "experience candidate phone call to see if they're worth flying in" part is definitely the one where I have the hardest time, being not in the Bay Area. I was lucky to find some great local people, where the cost was lower, because that's an expensive one to have to get good at fast. You lose a lot of nuance over the phone, though some other people in the company have been having very good luck with homework in this case - but as a candidate-choice option, where they could still go the traditional route if they wanted.
It's easier than it seems.
Just put a HackerRank test with a single question. "Print the numbers from 1 to 10 [inclusive, one number per line]".
20-30% of candidates won't attempt the test. 20-30% will be unable to give a decent solution.
I do agree that if people are flying around, that represents a fairly significant investment in any case. But in Silicon Valley, that often isn't true.
It's hopefully a case of coming up with processes that don't encourage people to waste others' time. But that also assumes some reasonable balance of power in the process.