It's unbelievable how they are so shitty at balance in the first place. Like, more grenades, enemies use healing items more often, enemies use buff effects more often, enemies get new animations and techniques the higher tiered they are/the higher level you are playing on. Enemy locations have "spawn points" (like huts in Borderlands where new bandits come out of) and the higher difficulty you are playing on the more enemies will come out. Add more effects to things. Like, bleeding and bandaging wounds. The higher the difficulty the more often this will happen. Increase rads given to the player the higher the difficulty they play on.
So many things that could be done to make the game more difficult and they went for a tried and failed way of "let's just bloat their health".
Seriously, I'm not exaggerating whenever I've said this: Bethesda is fucking incompetent.