I wholeheartedly agree with this, and I always thought leetcode questions and tech interviewing in general was broken, but as a filter for unqualified candidates, they were pretty effective. Which really matters when you have hundreds of candidates to sift through.

The biggest problem, of course, is that they also filtered qualified candidates (I personally got filtered out multiple times and I'd like to believe I was qualified!) But it is an understandable compromise whenever there is an extreme asymmetry in the volume of candidates and volume of interviewers, and the fix for that is simple: you study for the test (as you pointed out.)

Note also that as grandparent comment indicates, this test is a necessary but not sufficient condition; it's just to get your foot in the door for a deeper evaluation.