Well, I'm not sure how you're correcting for bias in the feedback. For the same reasons you don't think it's possible for an interview to be not-stressful at all; you also can't get feedback about that process without the bias that they're not going to want to tell you that your process might be bad.

You'd more or less need to get feedback only from people who are already happily and gainfully employed who are also close to neutral on the 'agreeableness' spectrum.

At any rate. You can remove the stress from an interview mostly the same way a therapist can remove stress from iterative therapy. By building an ad-hoc environment of trust, safety, cooperation, and goal alignment.

RE: Your Edit

Hiring is probably the most important thing you can do in/for any company. It should be a time investment on your part. If you don't feel like you're given enough time to do hiring correctly, then I'd suggest setting different expectations with your leadership about how to use your time or what quality of candidate to expect given the time you have.

Seeing a bunch of bug fixes across many projects tells you a lot about that person. So rather than going into the process looking for an extremely narrow thing (like some big project they are the sole maintainer of); go into it looking for anything that's there and see what kind of information is there to help you construct a useful narrative/model of that candidate.

Lots of bug fixes across many projects may not indicate that they can own a singular vision from start to finish (though you can assess that from getting them to tell you a story about literally anything), but it does tell you that they can read other people's code, supply feedback in the way of working alternatives, will take the initiative to solve a problem themselves rather than wait for the maintainer or someone else to get around to it, and focuses on getting things working rather than design-paralysis.