Yup. I saw some of this same sort of thing in the playtest for Silver Age Sentinels back in the day, where the designer's tendency to ad-hoc things personally colored how much he cared about vagueness in the rules, too.
But it can have even more subtle impact than that; the classic that's relevant here is how much some of the D&D 3e designers expected people to run games with it like they were playing 2e, rather than like what it seemed to imply mechanically, and then were startled (and misfired in some of their early adventures) when they didn't.
Which is one of the central problems of the "leave it to the table to figure out." Players will naturally read the materials available to them, and while some will always make choices without meaningful regard to their utility, most will at least
consider utility as part of making their mechanical choices. It is frankly foolish to expect players to never ever consider the mechanical impact of these choices (in 5e, things like class/subclass and race, spell selection, feats vs ASIs, etc.); even for players that consistently prioritize theme/flavor/concept over utility, there will almost certainly be near-equally-flavorful options at some points, and why would one choose the weaker of the two options if both produce good story of essentially equal quality?
Furthermore, why put players in the frustrating position of
having to choose between what is flavorful and what is effective and leaving the balance cleanup job to the DM? Flavor and effectiveness, despite claims to the contrary, are not mutually exclusive. Why not design so that, at least in most reasonably-expectable cases, things just work pretty well and do what they say on the tin, so that DMs only really have to worry about weird edge cases? It's not like D&D games are actually THAT weird and out of left field. We have a pretty good idea of what most people want out of D&D. Despite the lofty "you can do ANYTHING" rhetoric from many folks, tradition runs rather strong. Players tend to embrace certain kinds of novelty more than DMs, even when mechanically disadvantaged, e.g. Dragonborn have steadily grown in popularity over time (according to the D&D Beyond they've recently risen to 3rd, surpassing Tiefling for the first time in 2020, behind only Half-Elf and Human.) But semi-heroic, semi-comedic adventures in a pseudo-medieval faux-European henotheistic setting, where characters embark on "quests" (usually into dangerous wilderness, ruins, or underground locations) to recover/extract treasure/resources/people, save the day/stop a bad thing, or complete a contract forms the basic structure for the vast majority of play experiences. There will be combat, exploration at both large scales (overland) and small ones (individual rooms/spots), interactions with other sapient beings that do not need to end in violence, and lots of problems solved either by using a spell designed to solve that problem or by applying resources (magical or otherwise) to get through it. Both thematically and mechanically, these are pretty easily defined goals. Now, obviously some things will push boundaries, but the above is quite comprehensive despite this fact, and it isn't too hard to make rule-frameworks that are open-ended enough to encompass almost anything one might do in these spaces. On the thematic side, there have already been many settings that play with or reject parts of the established formula to one extent or another (Dark Sun, Ravenloft, Eberron, Planescape, Dragonlance, etc.), so all we really need do is give light-touch thematic support for the most common representation, followed by advice (ideally for both DMs and players, but definitely at least the former) on how to curate the thematics for different goals. E.g., a world where the only spellcasters are Paladins, Druids, Warlocks, and Artificers is going to feel different from one where no one can cast spells at all without becoming corrupted monsters unless blessed by the gods (but there are workarounds like Monk's ki). Or, a world without elves and dwarves, where the great ancient kingdoms were decadent but brilliant tieflings and industrious dragonborn bound by a rigid caste system. Or one where the only playable races are gnomes, halflings, kobolds, tengu, and other "small" races, as the Tall Ones died out long ago. Or any of a million other variations on deities/the sacred, the nature and prevalence of magic, what species/classes exist to play, and the overall technological development and societal structure present. This need only be a few pages at most--evocative suggestions and general guidance, for new DMs looking for that spark of inspiration.
...this kinda got away from me. Whole point is, I reject the notion that leaving known metaphorical holes or oversights in the rules is necessary for giving DMs the leeway to adjust things to suit their interests. I reject the notion that it is necessary (to say nothing of
good!) to make players choose between mechanical competence and flavor/story/theme. And I reject the notion that D&D is,
in practice, too diverse and open-ended to be designed reasonably well "off the shelf" for the vast majority of use-cases.
