Yeah, I had a 4e game where something like this happened. It was an enormous fight and if we hadn't blown all our "major" resources, people would've died (or at least rolled death saves--I only stayed standing because I was a Paladin, with survival abilities, and had two leaders backing me up). I'd really rather not repeat that experience in any game system at any point in the slightly near future.
I can understand your issues--they are, in fact, the "other side"* of my criticism of 5e's "short" rest. I think it's ridiculous that any more-or-less enclosed space--like a dungeon, a fort, a cave, an enemy village/encampment, or just about anything an Adventuring Party might explore that isn't a huge and trackless forest--can house distinct encounters that are widely-separated enough that a group can just take an hour-long break and not either (a) alert the entire area, (b) allow their enemies to replenish their strength, or (c) both. As a result, the majority of dangerous places strike me as woefully inappropriate for 5e adventuring parties--you're almost guaranteed to bring the whole thing down on your head, and because 5e is a numbers game, that basically means you die.
Of course, I haven't yet had a chance to see too much of this in action, but it's a major concern. The fact that you've voiced (essentially) exactly what I said, just from an (apparently) positive perspective,* increases my concern that it's true.
*I am assuming you think this is a good thing, whereas I don't. If that assumption is false, I apologize.