To me, the platonic ideal of a tabletop role playing game is this- a kit that is perfectly suited to building stories with a particular mood and theme.
Ideally, this hypothetical perfect ttrpg won't even require you to know what the theme is! Instead, it will provide you tools (mechanics) and materials (setting) that, in whatever way you put them together, will lead you to creating stories with the system's intended themes!
Of course, platonic ideals are, by their very definition, perfect, and thus impossible. So it makes sense that most games that aim for this ideal will need to signpost what sort of mood they want you to create, or even outright state it directly; an instruction booklet of sorts, to go with the kit metaphor.
But, it's definitely possible to attempt the impossible!
In The Magical Land of Yeld, you play as a group of children who find themselves trapped in a world of magic, surrounded by strangers- including monsters who are people and people who are monsters!
In Yeld, separated from their families and caretakers, your characters must take on Heroic Jobs, which give them access to new powers, and grow in agency and ability on their quest to return home.
To return home, your characters must defeat the Hunters of Yeld- powerful agents of the establishment who have pledged themselves to the ruler of this place, the Evil Vampire Prince Dragul- in order to collect the magic keys that will allow them to open the door back to their world.
There is a time limit, however- any player character who turns thirteen while in Yeld will transform into a monster, taking on a Monster Job which will empower them, but also change them for the rest of their lives and prevent them from returning home unless they take control of Yeld from Prince Dragul.
Did you catch it?
Nowhere in the game book is the theme directly stated, but as with all good stories, it's there, waiting to be found by those who look closely.
The theme of The Magical Land of Yeld is Growing Up.
You begin play as children thrust into a world full of problems, and given the opportunity to improve themselves and grow as people. You're introduced to many new people, and learn that while some of them are dangerous, many others are helpful, and what they are- monstrous or not- does not determine who they are.
Your characters grow and learn, gaining agency and responsibility as they do.
In order to return home, to "normality," you must fulfill that responsibility by working to make the world a better place, and thereby leave your mark upon it.
And becoming a monster, well… puberty can be a terrifying change that leaves you feeling monstrous, a stranger in your own body! As I mentioned above, being physically monstrous does not determine who you are! And with age comes even more responsibility- in this case, the responsibility to deal with the biggest problem plaguing Yeld, Dragul himself!
Even the basic mechanics of the system reflect the theme. The system encourages a round-robin GM style, which allows every participant to play both roles of player and GM, giving them the opportunity to grow themselves. The initiative system, with players declaring they will take the first move, then each making the choice of who will go after them. The action chain mechanics, wherein that choice of who goes when made collectively by the players can allow the characters to work together to achieve effects beyond what they would typically be able to do.
Of course, this platonic ideal of mine is not the only consideration that must be taken into account when creating a TTRPG. As games, it's usually assumed that a TTRPG will be "fun" and "enjoyable" to play. As art in a capitalist system, it's usually assumed that a TTRPG should be "marketable," "efficient," and "worth dropping money on." As creations often made by artists struggling under that capitalist system, it's usually assumed a TTRPG should be "something that will help its creator stave off starvation and homelessness under said capitalist system." These and other considerations are often why aiming for such a platonic ideal can be, at times, counterproductive.
(And of course, my definition of the platonic ideal of TTRPGs is not necessarily one that everyone, or even anyone, else would agree with :p)
But ultimately, I really appreciate seeing stuff that works towards this <333