Yeah, if you've spent a lot of time and effort building verisimilitude/immersion etc. that the world is a "real place" and what is encountered there is what makes sense to be there for the world, not encounter design, it can be tough to have a conversation talking game balance and design. I spent a lot of time building that image of "this is how things would be, I'm not designing things to be balanced," and honestly decoupling rests from sleep only HELPED me with that...I actually have a hard time having that conversation with my players, at least having it in that way. We are very focused on what makes logical sense in the fiction, and that often has little to do with exactly how many resource-expending encounters happen over a given period of time. What you're describing is a very anti-immersion conversation from our point of view.
But as you said, actually explaining the cogs and wheels behind the scenes can be tough and immersion-breaking.
I do sometimes wonder if my players think "you know, why was it a young dragon that confronted us and not an adult? Was it because we could defeat a young dragon but an adult would toast us?" Ofc I've had situations where PCs have encountered things they really shouldn't fight... But sometimes they DO choose to fight those things, and in 5e they can actually win unless the gap is 15+ CR.
Tangent: level 12-13 party, I thought "ok they'll have to non-combat their way through this to get the mcguffin from the dragons hoard; better make it ancient, they'll try to fight an adult and probably win." Turns out the idea of an ancient dragons hoard was too tempting, they're going to try to fight it even though I said that.. would be... Really really dangerous.
A5E Ancient Shadow Dragon is CR24... But they have some potent gear, summons, and boons now. If 5e has taught me anything it's that they might just slay it handily :')