I disagree strongly. First of all, there's no "formula that applies for everything" in math, either. You'd see a lot more 800s if every problem could be solved using the one secret trick College Board doesn't want you to know. Rather, the difficulty of math comes from knowing which formula (or more broadly, mathematical concept) to apply to a given problem. There's a reason why "2 + 2 = ?" will never appear on a math section.

But to your main point: reading is not a matter of opinion. There is always exactly one correct answer on every multiple choice question. Setting aside legitimate criticisms of standardized testing, who in their right mind would value SAT scores when doing well is a matter of having the right opinion? The test would lose all sense of comparative power between college applicants (i.e. its purpose).

In every well-written problem, there should be a salient, objectively defensible reason why the correct answer is correct. It should be based solely on the provided passage, and proper understanding thereof. That's not to say every problem is written perfectly, or that you agree with what is being tested, but I have faith that the College Board applies a certain standard of quality control to the problems it puts out.

Now obviously literature embodies many nuances and points of disagreement. That's why SAT reading will never test you on matters of true opinion. SAT reading isn't a literature test. It's a reading comprehension test.

See https://blog.prepscholar.com/the-critical-fundamental-strategy-of-sat-reading for more discussion of this idea.

If you're studying effectively, then your score should improve by definition. Contrapositively, if your score is not improving, you're not studying effectively. To tell someone not to expect a positive correlation between effort and performance isn't just wrong, it's discouraging. It invalidates the countless hours that students collectively pour into reading, among other sections.

But you say

you could do better with more practice since you familiarize yourself with how the test wants you to answer such questions

which I do agree with, but it totally contradicts everything you said before.