Back to chess, I am only interested in truth (i.e. the solving of positions to evaluate results and how to achieve them). Sorry for the offense this may cause. I am agnostic about the preferences of the chess composition field, and whether a position is an endgame study or a problem doesn't have any fundamental relevance to solving it: the objective and the rules of chess are all that matter.
Being interested only in the objective truth of a chess position is fine, and this probably parallels your preference for objective truth in the real world, i.e. the scientific perspective. If you're into philosophy, we can consider how most complex things have both a subjective aspect (e.g. artistic) and an objective one (e.g. physical sciences). Thus a painting has both subjective/artistic properties (in the minds of viewers) and objective/physical properties (its paints and wood). Likewise a chess composition, where its objective "truth" – win in X moves or draw – is uncovered by analysis or tools like tablebases.
The issue of soundness/unique play, though closely related to the artistic, actually belongs to the objective side. This is why, even though it's normal for problemists to have different (subjective) views on the value of a composition, they practically never disagree on whether it's sound. Soundness is on a higher objective level compared with the more fundamental "win/draw" lower level. Using paintings as an analogy, soundness is the colour/chemical properties while win/draw is the particle-physics properties.
It's fine to focus on the objective side of things, as scientists do, but this can be carried too far when subjective things are devalued or viewed as just illusions (e.g. emotions are nothing more than chemical processes in the brain). That's a type of reductionism common in the modern world.
 
     
    
 
     
     
     
    
 
    
The analogy of poetry is nice. Rhyming, numbers of syllables, and various other conventions are chosen by some and rejected by others. There is certainly no hard and fast definition of a poem, merely a body of work with various conventions. Some poetry looks like short prose to the average eye.
Back to chess, I am only interested in truth (i.e. the solving of positions to evaluate results and how to achieve them). Sorry for the offense this may cause. I am agnostic about the preferences of the chess composition field, and whether a position is an endgame study or a problem doesn't have any fundamental relevance to solving it: the objective and the rules of chess are all that matter. (That being said, knowing the conventions might allow clever reasoning that would help solve a problem - not of much interest to me).
Arisktotle's post said "To prove a fighting mate you'd need to provide all of the minimax analysis". Sorry to be blunt, but to prove a mate (I have no idea what the adjective "fighting" is doing there) you don't need to provide all the minimax analysis. Rather you need to provide a complete winning strategy, selecting moves for white (just one in each position will do) and dealing with all moves for black. You can ignore most white moves. This is how chess is played and more complex problems have to be solved by humans - there is not time to look at all possibilities for both sides, at least not at depth.