What is the context of this comment? Subjective language is totally fine in fiction, but unacceptable in academic writing, or at worst, unprofessional in non-fiction

The question here is unclear. What are you trying to write? Is it fiction, non-fiction or academic as per @MichalBurgunder’s comment?

@MichalBurgunder Yes, but I find that no text is free form this. And I don't mean that having objectively measurable things in academic writing changes anything about stylistic choices being subjective preferences. Also "clarity" is subjective (it's w.r.t. what kind of language you have been exposed to).

@mavavilj So what exactly is your question? This is still unclear to me. Sure, all language is subjective. Even the use of singular words is subjective, but what is your question regarding this observation? Subjectivity is not necessarily a bad thing, so there is no real problem to find a solution to in the first place.

@MichalBurgunder In a broader sense I never understand what's meant when someone says that "research paper X is difficult to read". I don't understand whether this means it's "not my taste/style" or it's "generally not appropriate". So if there are these subjective assessments on "what I think this language is like", then what can be done to "meet" differing personal tastes? I for example just finished my first large text and I made a conscious effort to go against "professional standards", which I viewed as "not comprehensible". So whose standard should we follow?

This analogy might not work, but sometimes this sounds the same to me as someone saying "I don't like rock music", which is useless, because it's a matter of taste.

@Mavavilj Oof, to be honest, deliberately "going against professional standards" because you disagree with them is a huge red flag. You need to write to your audience. The style rules you eschewed have been developed over generations by academics trying as hard as earnestly possible to do exactly what you're asking about: write papers that are as objective and unambiguous as humanly possible. Ignoring those rules has two effects: (continued)

First, you miss out on whatever benefits those rules give in making your paper objective. I really can't emphasize this enough: academic styles have evolved to prioritize concreteness and objectivity above all else. Second, and more importantly, your readers will know how to quickly read and understand a paper that follows the usual rules Even if your paper is somehow easier to read to people outside academia, your primary audience will have to spend more time figuring out how to understand your personal structure and style. And this will lead to confusion and misunderstanding.

@Kevin "their ease of understanding your priority". But to me this is easier said than done. What I'm essentially asking about is, how is one supposed to know when this understanding is reached? I've produced texts that some claimed hard to understand. I have no trouble understanding them. So what is one supposed to do then?

@Kevin Can you clarify these "usual rules"?

Blaming the world for something you struggle with is called 'projection', worse it avoids any real solution. You should ask about the individual "professional standards" you find "not comprehensible", rather than this contrarian rejection of all things 'standard' –– The back-and-forth in these comments suggests you want to argue about things that can't be changed. Without further context, Kevin has given you a good-faith answer. I'll add that you must meet a reader at their level if you hope to communicate. Rejecting convention to satisfy only yourself guarantees misinterpretation.

@wetcircuit If the convention is not based on objective reference, then it's open to subjective interpretation. I don't know, maybe I have too artistic view on most things. Natural language is not like programming language where it's possible to prove that some standard is more efficient. If we compare sentence style choice A and B, then I'm not sure if it can be concluded on. If choice A is held as better based on e.g. expert or my side opinion, then why is this not expert bias or subjective bias?

I have also read texts that were supposed to be very experienced in this convention and which I found very badly comprehensible. Which suggested me this subjectivity thing.

@wetcircuit The convention is also doing this projection, if it's subjective suggestion. Such as "I think that shorter sentences are clearer", "I think that punctuation A is better than B". What if there's a person who finds sentence structure B better or longer sentences better? Does this mean that the convention proposer projects his inadequacy of not understanding B and longer sentences? Or is language subjective? Up to what point?

I am not the one who's confused, and you haven't raised any gotchas. Okham's razor can best explain as a 'you' problem, not a 'society' problem. BE SPECIFIC: WHICH CONVENTIONS DO YOU NOT COMPREHEND (your words) or this is just hypocritically vague nonsense. When you identify your problem objectively and concisely, then we can maybe help you.

@wetcircuit The problem is what's a way of writing that's not based on subjective matter of taste. I'm confused about what's meant when someone says "text is comprehensible".

You could ask that person what they meant… Without context, I can only make generalized assumptions. A short story being called 'incomprehensible' carries a different expectation (time/narrative) than a scientific paper being 'incomprehensible', or social-philosophy. In a very general way, I'd suggest looking at the structure (whatever it is), whether each sub-structure is clear and delineated from the next, so the reader is well-oriented and focused on each point of relevance, individually 1 step at a time, to progress through the work. 'Incomprehensible' means they couldn't find any path.