Theory: The situation you describe is a common one across a broad spectrum of competitions. In some ways, school is a competition because not everyone will get to go to medical school, get admitted to the top law schools, etc. Think about sports where 1 point (or even 0.01th of a point in judged events) might separate a winner/winning team/champions from those we will never hear from again. It might even come down to a bad call from a referee, judge, etc. The GPA system you hate, for all its pros and cons, prepares you for "the way the world is" in many situations. That doesn't make it any easier, but it's hard to say that the GPA system you describe is going to hurt you in a major way. Medical school is no exception to this type of system of evaluation with its various "cutoffs."
For example, a small difference in ranking on a medical school application might translate into a big difference in medical school admissions. Let's say you were #201 out of a huge number of applicants to your top choice school. Let's also say they only admit 200. What the difference between #200 and #201? Applicants ranked #200 & 201 might even be virtually identical in terms of their ranked qualifications (same GPA, MCAT, school, activities, positions, interview ratings, etc.), and it came down to a mental coin toss to rank these two. Unfortunately, #201 isn't going to get in that year and perhaps never because there really are only 200 seats in the auditorium or whatever the more or less arbitrary basis for the exact cutoff count was.
Even if you fly past all the stages through life up through medical school, you might still just get edged out by just one applicant for a particular type of highly competitive residency (say Derm or Plastics) or maybe a particular program. Maybe your luggage was lost by the airline on your interview trip and you were more stressed than your nearest competitor in the interviews. The air conditioner rattled and you couldn't sleep a wink. Maybe you simply look a little too much like someone who was a very poor performer from years past, have the exact same name as the town drunk who ran over a 4th grader the day before or a wall street crook.
The redeeming feature in many of these situations is that you might have a handful of schools, programs, etc. you might want to go to and would be happy with. If you are that close to the razor's edge cutoff in one case, you could reasonably be on the "winning side" in other cases. If you are academically competitive (let's say you have mostly A's and some B's), do well on the MCAT, etc., you'll get into medical school, perhaps even to the school of your choice. It works out often enough, so to speak.
Life is often not "fair" in some sense. The situation you describe is perhaps much more objective than many other evaluations you face. You might get edged out for a position because your competitor is related to a famous person and other factors you have no control over.
However, chances are, everything is going to be OK in the end. In the off chance that this "B+" somehow bumps you off the track to the life of your dreams, you might find yourself on a new rail that turns out to be as good or even better in the end. It is very difficult to predict "what matters most" in a competition. The main thing is to focus on what you have control over and put your energy into those "high yield" areas where your efforts have the biggest payoff. Complaining about GPA systems is almost certainly "low yield" on the payoff scale.
Best of luck. I know these things can be very unpleasant at times, but it's sometimes better to simply keep moving forward, as difficult as that may be.
