I hate that as well. I HATED how hillbillies were stronger than mutant brutes in Fallout 3. So from my experience in Fallout 3 and other TES games, I just left Fallout 4 on normal difficulty level. Why Bethesda thinks bullet sponges makes the game more difficult mind boggles me. Maybe after 20 years that is all they know, and don't know how to make a game more difficult besides bullet sponges.
I hate to talk bad about Bethesda like that, I really like them a lot, love there games, but for me, this is where I see Bethesda fails. Bullet sponges does not make a game more difficult, just makes the game less fun.
So now I am not sure if I am missing out on not increasing the difficulty level to get those legendary weapons by playing on normal.