They gave the ripper and chainsaw the ignore dt cause game-wise, for melee -only characters that wanna kill the brotherhood.
The realism is a joke, the idea that a chainsaw/ripper could fully penetrate power armor is ridiculous.
But then again, realistitcally power armor should give you like +4 strength...cause it's powered and enhances your strength, like someone else said, being able to lift a car is a combat tool, the suit does the work for you.
I used to have a 6' steel rod about 3/4" in diameter with a chisel point on it. I could throw that right through a 60's car fender. Inner and outer sticking into the engine compartment. There is a reason modern armor is all composite. Even modern tanks field composite armor, Chobhamn armor is what the M1A1 uses. Your steel clad knights are far from real.
A modern Russia or US Exoskeleton is where realistic armor might go. Not really in service yet but go play Stalker for a taste.