Denny, I'm going to have to agree to disagree. Taking longer to kill something you already know you can kill only makes the "puzzle" take longer than it should and adds nothing to the cognitive aspect of the "puzzle". It's one thing to intentionally have enemies drain your resources by design, it's another to decrease player output and call it content. This is reinforced by trying to run non-combat plauthroughs and realizing "the puzzle" only has one answer and the real question is what language you want to say the word in.
We are specifically talking about combat, so non-combat play-styles aren't really relevant and are a separate issue.
Part of the combat puzzle is how much of a resource you use to solve said puzzle, and if that puzzle is worth the cost. It is also about how you trade off different resources to manipulate the the "worth it" line. Ammo is a resource, chems are a separate resource, but since some chems affect damage psycho can be represented as "use 25% less ammo". If you are flush with psycho and starved for ammo, then it makes sense to spend some of one resource for another. Melee is similar, since melee doesn't use ammo, but you take more damage at melee, you can trade health for ammo. Thus you can trade food, stimpacks, and a little bit of time for ammo as well, augmented with med-x you can cause that trade to also be more efficient.
Ultimately you can also just leave. If the camp/quest is too tough then you should just leave because the pay-off is not worth the cost. This is part of the game, because it isn't an FPS but an sandbox RPG. There is more than enough content that early on there are some things you simply cannot do. Many, many times there were Skulled NPCs at a camp or mission I was on, the solution was obvious, instead of spending time an precious resources grinding out a bullet sponge I simply left and came back later. It worked, that is part of the difficulty.
Now, they also undermine their own difficulty curve in many ways due to poor system design and balance as mentioned previously but manipulating basic stats, especially health & damage, is a perfectly acceptable way to scale difficulty.