This is an absurd characterization of coding interviews. I've been on both sides of big tech interviews, and I've been at a few companies. I've seen two extremes. At one end, the company had pretty lax interviews, and I rarely interviewed anyone while I was there. The quality of people at this company was relatively low, from my small sample size of coworkers. At the other end, a company well known for challenging coding interviews, and I regularly interview people. The quality of people at this company was relatively high, again from my small sample size of coworkers.

I think coding interviews are actually working fairly well. They divide people into at least two groups: a first group is people that can pass them without too much trouble, and they mostly seem to get hired, but of course there are mistakes. A second group is people that need to spend 500 hours cramming to appear qualified, and basically are trying to game the system. These people mostly don't get hired, and I suspect also are completely driving the conversation on HN and elsewhere about how coding interviews are a terrible failure.