Yeah I know what you mean, those normal weapons are really brutal compared to the powers of Hell lol
I finished Lost Mission couple days ago, It was pretty brutal but I got it done. I was thinking that RoE wouldn't be as bad as those refill bodies are everywhere like you said. I might give it a go too.
I'm not sure about the main game on Nightmare though as if Lost mission took me 3 days and clear time was under 2 hours so that would roughly mean I have 2 weeks of Nightmare ahead of me
Still I love Doom so I propably have to try it lol.