Spell slots and limits per day should be limits per combat because you can long rest after each fight.
And there is no way to prevent this without potentialy ruining the game for others ...
Danger zones? You just walk back and rest ...
Random encounters? You just walk back and rest ...
Timed events? You just frustrated people who will be unable to make all planned fights within single day, since all those quests are fail for them.
Respawn? You just created infinite loop for the same people.
It sucks ...
But i can see why Larian rather live with that their mechanics are "gamy" whatever that mean ... that with that they make the game unplayable for part of their playerbase. :-/
You're not wrong. There will ALWAYS be people who hate whatever they do. But leaving it as is also potentially ruins the game for others. So, of course, Larian must implement whatever will make the majority happy so they maximize on profit. That's not in question.
Regardless, since we don't know what that really is, we must still offer suggestions to help improve.
And bottom line, if you want the game to be more D&D:
You build encounters so that LR isn't needed to continue. Descent into Avernus. Cult of the Dead Three. Challenging to complete in a single go through, but it can be done with a few SRs, and help from NPCs makes it easier. Encounters are designed so that the party can get to the end without LR.
But bad RNG?
The DM helps them via NPCs or giving them more potions and items, etc.
But BG3 has no DM.
Well. True. But computers are smart and can assess character strength. "If Current Party HP is less than X%, have enemies you just killed drop X number of potions."
This kind of thing would encourage SR and discourage LR in BG3 especially if you tell the players that "you could turn into a mind flayer at any second.". And if they do LR spam, you hit them with a strange dream - a Dream Lover dream. Or, you have something happen at the grove to let the players know, "Oh dang. Time is a thing. I can't just willy nilly rest. I need to be smart about this."
So, 2 key ingredients:
1. Encounters that don't require or encourage full rest in between on a frequent basis - like the Underdark in BG3.
2. Consequences if players LR too much - minor at first to give plenty of warnings and then more harsh if it continues. Consequences that make sense.