This does have useful info in it - the line starting with "But tech-wise". I think you're right that technical feedback is the biggest thing, and even a binary

This does have useful info in it - the line starting with "But tech-wise". I think you're right that technical feedback is the biggest thing, and even a binary answer is useful. "Cultural fit", "we found someone better", and "the boss' nephew got the job" are all somewhat interchangeable from the candidate's perspective, but "we didn't think you could do the work" isn't. For a company willing to provide information (and yes, most seem to be scared of the legal issue), that's the most value-dense thing to provide.