It seems to me that one of the questions to ask is why the hiring process so difficult ? Are candidates not qualified ? Or does HR really understand what they are looking for in the first place ? It is probably a combination of many things of course, but this adverserial relationship is counter - productive at best.
It is HR's job to stop those at the gate who are obviously not a decent fit, it is easy to see ( at least for me ) whether someone will be a good fit in the environment during the interview.
Often this important element of filling positions is badly missed by would be managers.