Interesting post. Agreed that it’s totally unfair to put candidates through all of that. I’ve been on the other side (as an interviewer) many times, and it’s a difficult job. The trick is to find what the candidate has been doing and focus on that area, dig deeper and find out how much they have considered about their problem. In some cases it’s a great learning experience for the interviewer (and I don’t mean in an industrial espionage kinda way).
If you find the process is purely focused on the company’s specific problem domain (or even worse, some random domain0, then I would see that as an immediate red flag. Not all companies are like that though.