Which begs the question why test engineers with leetcode trivia bullshit. You are yourself emphasizing why their interview process (and they are just one of many offenders) is so bananas inappropriate.
https://www.darkcoding.net/software/facebooks-code-quality-p...
https://blog.timac.org/2017/0410-analysis-of-the-facebook-ap...
Granted, perhaps things have gotten better in the last five years.
It's certainly possible for an enormous engineering company to have poor code quality or poor engineering practices, despite having a high interviewing standard. And a criticism of Facebook need not be a criticism of all companies that interview by Leetcode, for instance no one here is criticizing Google, Amazon, or Apple, and all have better reputations for code quality.
[0] https://www.reddit.com/r/iOSProgramming/comments/6upeu6/how_...
[1] https://www.facebook.com/notes/facebook-engineering/under-th...
You’re describing the attitude Facebook takes towards candidates, not the attitude I take towards anything.
Candidates should be saying to Facebook, “ I really hope all of your code is perfect every single time to be acting so high and mighty” and absolutely making a huge deal out of a case like this when it isn’t.