> Even for candidates for whom my feedback was scathing, they are still generally positive about the experience

If you have scathing feedback for someone you are interviewing, you should probably just shut up. Or at least deliver it in a different context where they aren't being held hostage and having their every reaction scrutinized. Sounds miserable, I seriously doubt they were actually "generally positive"

As an interviewer, it's my role to get the information I need to help inform a decision that I will not make alone. If I have a concern about some unknown, I have to navigate that; it's on me. I expect an interviewee to be prepared to share relevant information, but interviews are stressful and if I only want to hire good interviewers, I'm going to have a considerably smaller pool.

Furthermore, as an interviewer, my job is to be a candidate. Why should this person choose my team/company to work at? It's a privilege that anyone show up to join, and I ought to be as prepared to give answers as they are.

That said, any "feedback" I would give would be arbitrary. I am not this person's mentor and I shouldn't—after only 40 minutes—assume I know enough to give them feedback. Saying that I have concerns about not getting enough information, and that somehow being their "feedback," is bad framing. Try:

  Before moving on, I really want to make sure I get a full picture of your time at Acme working with the Foobar team. Would you say that you led project X? Who ultimately decided when it shipped and set deadlines? Was that part of your responsibilities?

I'd recommend avoiding giving anything framed as feedback altogether. End interviews by saying "We're all finished with this part of the interview. Thank you for taking the time to go through your work history with us. You should be hearing from [Hiring Person] about the next steps."

I know TFA mentioned similar things about also being a candidate and that the "feedback" is to spur discussion, but the framing of giving "highly opinionated" thoughts about someone's capabilities as a way to ask questions is unnecessarily adversarial is an already power-imbalanced situation. I think it's better to try to tilt the power imbalance in the other direction—giving the candidate a feeling that you, the interviewer, are also auditioning for them. Doing that shows humility and, in my experience, gives a better opportunity to get to honest answers about being a good fit for each other.

> Ok. It’s not really a question. The ‘is that ok’ isn’t really seeking permission; it’s giving the candidate a few seconds to prepare for what’s coming.

Oof, what the hell? I'm not a big fan of people who want to offer feedback but don't genuinely ask first, and accept that the person might say "no". (And then honor that!)

Some of the feedback the author described wasn't really feedback, it was more like they didn't fully ask the questions they wanted to and should have during the interview, got the wrong impression, and then thought that offering feedback was the way to get that fixed up. No, the right thing to do is immediately ask a direct question about what you're looking for, at the point in the interview when you aren't getting it.

By the time an interview ends, a candidate usually has a good sense of whether it went well or not. I've interviewed hundreds of candidates and I would never jump into this feedback mode OP describes. There's not much point in giving positive feedback if they're already feeling good about the interview. If you give someone negative feedback (no matter how constructive) they're going to get defensive and want to plead their case; but it's the end of the interview and there's no time for that. OP says people express gratitude for the feedback, but what does he expect them to do? Anyone who doesn't appreciate it still doesn't want to tank the interview by appearing ungrateful. Never play psychological games in interviews.

> “ You seemed quite nervous”

This kind of thing is weird to call out. Your perception of a candidate’s emotions isn’t relevant. People are wired differently. Some people can bullshit with no nervousness at all. Some people can be highly skilled and not able to practice this away. It’s a matter of wiring.

Calling out actions and behaviors and words, observable reality, is fine. Emotions, no.