This sounds like a recipe for an incredibly inconsistent interview process. I know engineers love open, discussion-y interviews and senior interviewers like gi

This sounds like a recipe for an incredibly inconsistent interview process. I know engineers love open, discussion-y interviews and senior interviewers like giving them, but the evidence just doesn't bare it out. "Work sample tests" and "Structured Interviews" are the most predictive of on-the-job success from the published research I've seen. No matter how much I'd prefer to have a freewheeling conversation as you describe, I have to bow to the evidence.