So as a hiring manager I am pretty OK with rejecting a lot of good applicants just because some little part of the interview didn't go well, if it means that I never hire anyone really bad. The good applicants will get jobs somewhere else, it's OK.
The technical interview is part of that. The coding test is part of that. Sitting down with them and making sure they can talk through a problem with their future teammates is part of that. There's no one piece.
And finally, if your career is to write code and solve problems, and someone gives you a test where you have to write code and solve problems, you should be elated. Is there anyone that wants to answer the "Tell me about a time where you had a disagreement with a supervisor"-type questions that the rest of the world has to deal with?