[filoleg]

>I've rejected a good bunch of candidates that can pass coding tests while not having any good understanding of theory, hardware, OS, networking, security

Those are valid points, fully agreed. I think the discussion of those topics must be included in an interview process and discussed in-depth too, leetcode-style problems are not sufficient enough on their own.

>Leetcode focused on tricks and memorizing algorithms.

Strong disagree on "memorizing" and only partially agreed on "tricks". Those "tricks" (like knowing that you should use a hashmap when you need a key-value datastructure, or memoizing [aka caching] repeated operations) are very useful in real life problem-solving situations at work. I can tell you for a fact, I don't remember almost any particular problem from leetcode, and I ended up solving certain problems multiple times on leetcode, because I couldn't recognize them at all. However, thanks to leetcode, I obtained a pretty solid intuition on which approach to use in a particular situation, and it helped me out in the workplace immensely (even if I don't directly implement those approaches or remember the specifics 99% of the time).