I was confused about interviews in big companies before. Especially sometimes you have interviewers from not the hiring team. I was also confused about how leetcode questions are used, and sometimes feel that justification on hiring or not hiring are not based on evidence. Then one day I changed my view. I am seeing interviews a way to evaluate candidates' wanting to a job, and his effort of trying to achieve something. If he can invest in time in leetcode, he definitely can learn and do well in any tasks. We are humans, and we can improve. So the interview does its job. Nothing is perfect of course.
The issue with Leetcode and HackerRank as I see it, is that you're reproving to various companies each time and each interview that you know how to code. However, the only alternative to this seems be an SAT for programmers, which isn't better.
To be honest, coding is not difficult. Also many jobs do not require 'that' much knowledge of low-level informations anyway. Especially nowadays, for most positions, you don't need to know re-ordering lines of code can affect the cache, you use hash whenever it is possible and do not need to implement your own data structure. If you do need something in your work and you currently don't know, google and reading will definitely teach you. Programming is not a special power only few people can have. Actually, if you are consistently learning, you will probably do well in any tasks. If people are not willing to put some time into getting the job they want, maybe they don't want the job enough.
