I barely passed my DELF B2 ages ago (barely means 50/100, ages ago means 2010). I hadn't prepared for it specifically either.
While I'd partially agree that it is weird and slightly skews the reliability of the exam, when some people just drill the exam preparations and are not as good at anything else, I think those people are still exceptions. Since then, I have definitely changed my opinion and take the exam preparation as an opportunity to broaden my learning focus and learn new stuff. My DALF C2 preparation definitely came handy in real life too, and I don't think I would have learnt some of the things I normally use without the exam. Refusing to prepare for a DELF/DALF exam may feel like being heroic. But in reality, you are missing out of the best coursebooks focusing on very practical use of the language, and really pointing out stuff you don't know you should know.
I remember my oral exam going badly too. Partially, the testing centre was to blame, as they broke the rules and one of the two examiners was simply absent during my exam. She went away, when I came to the room, and came back at the end of my exam. Back then, I didn't have the courage to protest and it made me really nervous. Also, I had been prepared for a shorter monologue and then discussion, but it turned out to be the opposite, it was like talking to the wall. And even the dialogue part was weird with that one person. But yes, I wouldn't have gotten an awesome score under any conditions, given my skills, but I wouldn't have been so bad either. Next time, I'd recommend looking on youtube, there are various videos of the exam candidates, often with evaluation and tips. Such videos are a very good lead, during the preparation
Writing is the most difficult skill to prepare. The learning resources totally underestimate it, including teachers. As a way to discover a lot of the imperfections yourself, I'd recommend putting the paper aside for a few days and then looking at it with fresh eyes. You'll notice a lot of stuff. Also, writing with a stopwatch is an extremely useful exercice.
You are not supposed to understand tv series at B2, I don't know, where people get this belief. And a few hours of tv series make no difference. A few hundred hours, however, will bring your comprehension to C2.
Careful about the tutors. B2 is still not that far, but when you are at the higher levels, ask about their experience with the learners at C1 and C2 and the exam preparation. And demand direct answers, no vague sauce. Most tutors are simply not strict enough for the advanced learners.
About her doubts concerning your reading: this is unfortunately normal. It happened to me repeatedly, that teachers were underestimating what I could read. Back when I was still in class, I used to believe them (and nonsense like this is one of the many reasons, why I don't trust teachers anymore). It slowed my progress down by years. Teachers are often heavily prejudiced against reading (especially extensive reading, without boring yourself to tears by dissecting every word) and seem to be extremely ignorant about the difficulty of various books and about the reading effects in general. L'Étranger was my first book in French too, ages ago at the B1 level. I really disliked the book.
I would have disliked it in any language. It was a challenge but a totally normal one, not too much.A piece of advice: if you want to use tutors, do not take their advice too seriously. At least not unless they have reached C2 in another language or got some people there (and even then, take it with a grain of salt), they simply don't have the needed experience in many areas. Yes, use them for speaking and writing feedback (and use the strict ones, not the lenient and too encouraging types), but don't let them slow you down or discourage you from a challenge. They simply have no clue about the advanced learners, they tend to believe that broken B2 is the ceiling of what a foreigner can achieve and act accordingly.
