With a smaller plant you definitely do not want to remove heathy leaves. In general never remove more than 10% of the leaf area at any one time. If the newer leaves are smaller then the spot you have it is definitely too dark.
And to answer your original question, “Why is plant knowledge voodoo?”.
There literally hundreds of thousands of plant species. Each of those species is adapted to different environmental conditions. The requirements the species need are further modified by its interactions with micro-orgsnisms. So the answer to most questions about growing them requires an significant depth of theoretical and practical knowledge on the subject.
A large portion of humans quickly revert to mythology when any topic becomes slightly complicated.
It’s a shit ton harder than people realize… well at least to go anywhere in the industrialized world. Unless you are independently wealthy or have an extremely high demand job.
Billy Bob who’s career is working at McDonalds isn’t going to get approved.