The glaring problem (IMO) with throwing hard LC-style questions at interviewees, is that it's a fundamentally stressful and high-stakes situation - which is so far removed from the actual working environment.

What are you actually inferring from the situation - how well the candidate can write software? How well they tackle stress and anxiety? How much spare-time they have to grind these types of questions? etc.

Probably a mix of them all, but there's a lot of irrelevant noise - if you're just looking for one thing.