This has the implicit right answer: A job interview is the worst moment/place for feedback. There is just too much heart/animosity at stake on both sides.

I've been interviewing candidates for more than 15 years (for PhD /RA positions and then for Engineering) and every time I've given honest feedback, candidates just get into an argument on why they think the feedback does not apply to them...

It is just not worth it. If I want to know how am I at certain skills... I test myself in a less "charged" environment.

That means that in 15 years you have not learned how to give not honest busy constructive feedback.