You do know that 4E's "nuke" abilities refreshed daily, just like in the vancian system?
Well, D&D's brand wasn't that rigid, it was more like the fantasy RPG that everyone customized to his liking, and from which other games took their inspiration. (Also mechanics can't be copyrighted, so they can't be "brand identity" from a legal standpoint.) Vancian casting might've been the default but there is a good proportion of the player base that wasn't satisfied with it. Two obvious reasons come to mind: 1) not every setting was compatible with the vancian idea of how spellcasting works, i.e. that preparation/memorization is "locking mystical energies in the mind of the Wizard that are expended and wiped from the Wizard's mind when the spell is cast" (AD&D and 3E), so that you couldn't even cast twice a spell you had memorized once; and 2) not all adventures worked well with a daily refresh of abilities, which presupposed that you'd do multiple combat encounters per day, rather than one per week for example. Also, it didn't make sense and work for every adventure that you couldn't take the time to change your prepared spells during the day (say you have 5+ gaming sessions happening during the same in-game day). Many houseruled those things.
True, 3E moved all the talk of rule customization to the DMG, and that was a weak point in its presentation. It definitely led to rampant arguing over the RAW on the WotC forums, over what is the correct rule rather than what ruling you use in your group and why. Sold more books though, since people craved for the official word above that of their GM/table.
Well, classes and races have always been well-defined archteypes, and that's enough. No need for ability score requirements to have that, for example. 3E was clever about how to mechanically model those archetypes, introducing ability score adjustements for races and favored classes rather than class limitations and minimal ability score requirements. That is a more flexible approach than AD&D, that maintains the well-defined archetypes.
Well, this progression you like about the Wizard, from zero to God, does not require a vancian spellcasting system to express. It could easily be done with a different mechanical representation of that idea. The alternative is not just potions/cooldowns. All the alternate D&D spellcasting systems prove it.
D&D from the beginning had as an intended end-game that the player-characters should build strongholds and rule dominions. However, the original rules contained only a few pages detailing this aspect of the game, and AD&D was similarly lacking in this regard despite a much larger number of pages in the core rulebooks. It wasn't until the publication of the D&D 'Green Box' Companion Set in 1984 that semi-detailed rules finally existed for dominion rulership, but AD&D 2nd edition failed to continue this, instead again providing little explanation of how this aspect of the game was intended to work.
I think 2E DMG plus The Castle Guide covered that well, especially castle construction. There wasn't much on kingdom management, but that's a different sort of campaign.
It does have a limited appeal, but Birthright showed it can be fun.
True.
I think it's rather that it's just a different gameplay. And because the class system makes every character be built as an adventurer, as someone that is supposed to work in a party of a handful of dudes with complementary powers to kill monsters in dungeons, D&D characters aren't adapted to such gameplay. You can try to add systems to D&D to model that, give class options and stuff, but at its core D&D classes are made for tactical combat, most of their abilities serve that purpose (plus a small amount of related activites -- getting access to quests and loot). For dominion ruling to be the gameplay focus, you'd need a different character system and an entirely different approach to encounter design, since they most likely would involve social / political challenges rather than tactical ones.
Dominion rulership tied back to the origins of D&D in miniatures wargaming, since the player-characters and their troops would become involved in various conflicts that would necessitate mass battles. These could be resolved using Chainmail rules for medieval miniatures (predating the publication of original D&D, though a final revision occurred afterward), or the D&D War Machine rules found in the Companion Box Set (an abstracted approach), or in the AD&D BattleSystem Fantasy Combat Supplement (new rules for miniatures battles). Both warfare and management of dominions were supplements to adventuring rather than replacements for it.
