Oh boy, my advice would be do not ever do this again. In fact, if you were anyway rude or inconsiderate or disrespectful or even entitled in this email (which it’s hard to believe you weren’t), then I think you should apologize.
It’s just a really bad habit to get into. There will always be someone who ticks you off, someone who does something that you think is unfair (regardless of whether it actually is or not), or someone you just want to “take your frustration” out on, but you can’t (or, I suppose, shouldn’t). What if this was your boss? Would you rant at them over an email? You also never know when bad relationships with professors can come back to haunt you. This professor could teach another class you are in or be in charge of a research project you want to get involved in or just be close friends with other professors in the department who could hear this story. This isn’t the kind of behavior that you want to get used to nor is it the kind of behavior that you want to be known for.
If you want to vent, do what everyone else does–complain to your significant other or a family member, rant to a friend, even post something (anonymously!) on the internet if you have to. Don’t complain to the professor who gave you a good grade that you earned for the work that you did.
This is actually something I tell a lot of high school students when they ask what makes college classes different. One of the reasons college classes can be more challenging is that many classes become more test-focused (or in some classes, your grade might be very dependent on a final paper or something similar). I would say the vast majority of my classes had 100% of the total grade determined by exams, usually just a midterm and a final (although, sometimes, there were two midterms and a final, and rarely, my entire grade was just based on the final exam). You’re absolutely right. There’s less room for error. You can’t expect to get an A when you only get B’s on the exams, like you might have been able to get away with in high school. You’re expected to perform on exams, and for many students, that can be really difficult. Not all classes are like this, but as you’re finding out, it’s much more common in college than it was in previous years of schooling.
It can also be frustrating when you miss the cutoff for a grade. I get that. But you have to draw the line somewhere, and you didn’t earn an A. That’s really okay. I had a class once where the cutoff for an A- was 93, so in that class, you would have gotten a B+ with your 92.4. Take your A- and move on with your life.
Don’t blame your professor for this. It’s really not their fault, and complaining to them over email is not going to make them want to do you any favors. It’s going to make them much less likely to help you in the future.