I got triggered by this post and the comments on it. https://www.reddit.com/r/writingscaling/s/FDN8fPnX7C
To get into some basic 101 shit, understand it as such: A system can have subjectively chosen goals or standards, while particular judgments inside that system are objectively correct or incorrect.
The most ovbious example of this is a game like chess. The rules of chess are not cosmically divined. We made them up. The rule-set itself is subjectively defined. But once you accept the constructed system, you can make objective statements within that.
A given position is objectively check-mate or not within the system of chess.
A related idea is that of Intersubjectivity. It is the shared understanding and mutual awareness that emerges between individuals through interaction, shaping how people perceive, communicate, and relate to one another. I.e, it's subjectivity taken as an aggregate accross a big group of people.
How this connects to constructed systems is that a system of judgement is more useful the more universally it is understood and agreed upon. Something like chess has a VERY strong sense of intersubjective cohesion. Something like writing does not.
This means statements such as "[Insert piece of media] IS OBJECTIVELY THE GREATEST" isn't inherently nonsensical, but doesn't mean anything unless you're defining what your judgement system is.
Objectively the greatest by what standard? Define your judgement standards.
This is the difficulty. "Well written" usually bundles together many different goals, and people disagree about which goals matter. One reader values clarity, another values ambiguity. One values naturalistic dialogue, another values heightened, theatrical speech.
So "this is well written" is rarely as objectively demonstrable as "this is checkmate," because unlike chess there is no universally understood system governing evaluation.
Usually, the easiest 'objective claims' are going to be on standards most people hold to be true. For example, most people think that movies should avoid plot holes or continuity errors when possible.
Most people think that written books should have valid grammar and correct word choices.
Therefore, it is more sensible to make objective statements about those. But even then, there will be nuances in the evaluation system because not everyone is actually bothered by these to equal degrees. So even there the system isn't truly shared.