Agreed, this is why I give my own coding quizzes, so I can have a discussion about it. I'm more interested in the thinking than the answer.
But, I do have sections in my interview that test knowledge and not skill, so I can still see the usefulness of letting Hackerrank be a part of the process.
The one thing I don't claim is that HackerRank or coding quizzes are perfect. This is why coding quizzes are only one of maybe six phases of an interview.