It is incorrect to label the current D&D system as Vancian. I keep having to make this point. Vancian casting involved taking each spell and charging up that spell, and that spell only, for release at a later time. There was no swapping spells between slots.
The current D&D system is a spell slot system, not a Vancian system. The prepared classes (paladin, cleric, druid, wizard) still swap spells in and out, while the known spell casters (rangers, sorcerers, warlocks, arcane tricksters) cannot. Please don't call the current system Vancian - it isn't - it is at best vestitial vancian but really deserves its own name.
To understand Vancian, please review this. See also this.
Spell slot system versus spell point system is a far better pair of categorizations, as would be a mana pool system ...
As an aside, the HP systems in various games also represent resource management systems. (Crap, I have forgotten how the health/wounds system in original Traveller worked, now I need to dig the boxes out again).