To be clear, at Firebase, we held these kinds of discussions in addition to the technical assessment. A portion of my section of the interview process was usually to do a deep dive on a recent interesting project that the candidate had worked on, either sourced from their resume or just by asking. You're right that you can often tell their level of involvement by seeing how quickly the well of details dries up.
There are tradeoffs, but I found it to be an overall net positive in addition to the technical assessment. Doing this effectively requires that the interviewer have a pretty broad exposure to lots of different technology, otherwise you can't distinguish between someone BSing their role vs something you just don't know a lot about / can't ask intelligent questions about. It's also incredibly subjective, which would make me hesitant to rely on it without more objective criteria.
There are tradeoffs, but I found it to be an overall net positive in addition to the technical assessment. Doing this effectively requires that the interviewer have a pretty broad exposure to lots of different technology, otherwise you can't distinguish between someone BSing their role vs something you just don't know a lot about / can't ask intelligent questions about. It's also incredibly subjective, which would make me hesitant to rely on it without more objective criteria.