I would say that in the case of D&D-like games combat is definitely a reward and not a penalty.
You’re assuming trad play, but that’s not what’s being discussed.
@Retreater is right, I’m talking about old-school sandboxes (or, rather, OSR play). In that style of game, encounters aren’t designed with the capabilities of the PCs in mind. Newer ones are emphatic about that.
For example,
ENNIE-nominated adventure
Halls of the Blood King is for character levels 3 to 5, but it notes as the very beginning:
This adventure is suitable for PCs of 3rd to 5th level. Note that, as an adventure in the old-school style, not all encounters are intended to be balanced to the PCs’ capabilities. Judicious use of stealth, parley, and trickery are to be encouraged, in place of blindly rushing into combat.
Many of the creatures you’ll encounter are 3*–4* HD. The
guests they’ll meet are 7** HD or more. The adventure also has a time limit. This isn’t
Curse of Strahd where the tracks are carefully laid to a climatic encounter with the main villain. If the PCs want to win (whatever they consider a win), they’re going to have to be clever about it. Getting into a fight, especially a fair fight, is indeed a failure state.
One issue that Pathfinder 2e has with this style is that it just doesn’t work very well with attrition. With enough time, the PCs can heal up fully from any fight (no matter how foolishly picked). You can try to apply time pressure, but that doesn’t work well as a general approach in my experience. For example, taking a little bit of damage in a fight is trivially healed at almost no cost.
I
mentioned it in your threat on healing, but I’ll repeat it here: the system strain mechanic from SWN/WWN does a good job of balancing access to healing with making that have a cost. Healing wouldn’t be any less accessible (in fact, I’d just let them Treat Wounds as much as they wanted at the end of combat), but you could only take so much before you had to stop and rest.