"Can't be standardized" is something of a red-herring, as I've encountered a huge variety in how even algorithmic questions are presented and judged.

[More] prone to biases and opinions? Let's assume this is true (I'm not convinced that it's such a slam dunk - someone who wants to say no to a candidate can find a way, especially if they aren't being shadowed or recorded (which would feel pretty draconian for the interviewee too)). Isn't it still just a way of making a lazy complaint, "but that's harder!" You as hiring manager are responsible for knowing yourself, knowing your interviewers, knowing their strengths and weaknesses, and knowing your own.

That makes it hard to assembly-line interview fresh graduates, but maybe you should have a separate process there anyway because they won't have much in the way of useful experience yet anyway.