A lot of those "what ifs" seem to be unfipping the squad/army based war gaming ->but now you get to control a single unit and focus on that unit's experience switch that d&d started with. Those seem more macro level things than d&d really handles.I know, and I agree with you that "press on or rest" is (or should be) an interesting decision point for players. I don't think it follows that "therefore resting should take days of game time and rather a lot of play time committed to busywork." The game logic alone applies narrowly to a specific kind of military scenario--one in which there are clear advantages to sustaining pressure on an enemy that wants to buy time.
The game logic doesn't apply particularly well to other kinds of military scenarios. What if the pressure of an invader has united the enemy, and relaxing that pressure will cause them to fall back to infighting? What if there is no common, united "enemy" at all? What if the enemy is so big and the problem on such a scale that the party can remain in Rivendell as long as it takes? All the clerical BS is just delaying the cool Council scene that's coming next. What if it's an exploratory expedition such as a hexcrawl, where pressing on into the unknown with insufficient resources is simply foolish? What if it's a pulp Sword & Sorcery adventure where the pacing between Act I, Act II and Act III should be fast and furious? What if the PCs would otherwise press on to the next level of the dungeon, but because they know they have days of recovery and clericry ahead of them, they choose to withdraw early and get it over with before delving deeper?
From my perspective, this is something very common in the OSR, or among dedicated old-school players in general: The idea that a particular game dynamic is cool, and therefore that the weird/wonky/idiosyncratic way it was handled in the classic rules is genius, actually. The best OSR stuff identifies the cool game dynamic but isn't afraid to explore different ways of handling it.
Anyway, so as not to be a complete thread derail, Shadowdark still feels old-school to me and still gives the DM a terrific, much more flexible toolbox with which to present that "press on or rest" decision point while still using 5e's "full heal on rest" rules. In 5e itself, IME and as I said upthread, attrition pressures scarce resources (daily uses and spell slots) long before it pressures hit points, so even if you value the attrition dynamic, buffed healing spells shouldn't be a big concern. It might enhance the game effects of attrition by blowing through spell slots more quickly!