The issues with combats is a bit more complex that "they heal out of combats". They should probably heal out of combats and we should certainly not be able to kill them while everyone is "out of combats".
If minotaurs and bulette are extremely hard, it's not because you can't exploit mechanics anymore... It's because they are way too powerfull.
If they are OP it's because they would be too easy for players that use the OP mechanics...
These combats are extremely frustrating but you know... Choices have consequence so something else has to change, leading to other consequences...
Larian has created this issue with their own design:
DOS combat mechanics, caused them to try to increase monster abilities and such to compensate for DOS not being compatible with 5E rules.
Then to try and compensate for everyone abusing broken stealth, they introduced healing out of combat.
If they'd started with 5E, and only modified what needed to be modified to work better in a videogame, instead of starting with DOS, then they wouldn't have this plethora of issues that they are now playing whack-a-mole trying to compensate for.
