Difficulty is very subjective to players, aswell as how to best balance it.
Some people want scarcity. Low caps, constantly having to make tough calls on what to buy. Low ammo a constant threat that the next big fight you might just run out.
Some people want volume. Lots of enemies, they don't have to be tough there just have to be a lot of em. Fight the tide!
Some people want few enemies, but they should be hard to beat. They need to be constantly flanking you just when you reload. How do they always know!?
Some people just want enemies that are tough as nails. Like, seriously, that is the third clip. Did his healthbar even move?
Some people want entirely new mechanics. The enemies are not the biggest threat in a wasteland, starvation and dehydration are the real number 1# enemies! You can shoot a radroach, can't shoot hunger induced paranoia.
Ultimately it will come down to modding for players to really find what for them is their personal sweet spot. But even without mods there are choices i, as a player, can make. I'd skip perks like Scrounger if i want rarer ammo and caps, or i'd not bother with crafting if i feel i'd end up with to powerful weapons to early on. To give some examples.