i think this is /less/ of a lore problem, since if you want (at least terminator) power armor to be able to give you spatial awareness and biofeedback then it seems more plausible you could at least sort of track some kind of semi-accurate shoot from the hip fire
but also you are giving up a pretty big advantage which is that space marines are tall
like really tall. taller in power armor
the height advantage when shooting gets negated if you can barely lift your arms to boob level














