OK this idea just occurred to me, so it is a rough draft, but it attempts a new approach to healing that bridges the conflicts between ‘realism’ vs. ‘gamism’ and between magic vs. natural healing.
Between battles, parties with magical healing capable classes (i.e. clerics) can heal their party to full HP during a short rest, using their magic healing. Without magical healing, no hit points are regained while adventuring. Only magic or time and rest can heal injuries. During a battle, all normal healing spells and magic applies.
The great thing about this re-setting of hit points during an encounter is that HP no longer become a resource to be spent and saved, but return to their natural place as an indicator of the amount of punishment an individual
(or swarm) can take and/or has taken.
There are plenty of other resources to be managed and honestly, getting people to rest between encounters has never been a problem, just the opposite is usually true. Therefore, with a cleric, druid, paladin, or whatever, hand-wave the fiddly in-between encounter healing and they just do it. Now encounters can be based on a full strength party rather than an estimate of how ‘spent’ they will be when engaging.
Other mechanics could be added to limit the amount of times a cleric can do this in-between magic. Like a low level cleric may only be able to do it one person per level per hour or something similar. Possibly druids or bards even might be limited to curing fewer times, or less than 100 percent. Or maybe every time a healer uses the skill, they lose a point of strength (they take on the pain like an alien chick in an old episode of Start Trek) until they are forced to rest. These types of rules however ruin the basic premise that the party starts every battle at full hp, and when a character is not at full hp they are in fact injured, and a night’s rest will not cause gaping wounds to heal.
This is all just theoretical at this point.