[extr]

This reminds me of an data science interview I had early in my career that was exactly along these lines. Several "case studies" that turned out to be semi-guided math/cs interview problems. One guy started off on a variation of the secretary problem, I recognized the general form of it and pointed out that there is a straightforward way to derive the optimal solution, which we could tweak for our situation. No no, we have an hour to kill. I want you to explain my way of solving the problem back to me. Cue an hour of frustrating whiteboarding where neither I nor the interviewer seemed to really grok the intuition for the steps we were taking. I went through 3 more situations like this over the course of a grueling 8 hour day, probably about an hour of which I had the chance to talk about my own background. Didn't get the job, and was specifically called out for my "poor technical performance". I had been through so few interviews at that point I had no idea it wasn't the norm. I legitimately wondered if I was cut out to be in the profession. Felt like major shit.

A little while after I had an interview more like what you describe. It was night and day. We did a brief technical portion that was mainly to ensure I wasn't bullshitting my experience level, then a few hours of discussing my past projects with various current team members. I actually enjoyed it, found myself relating to my interviewers, and easily got the job.