The arm width looks fine compared to the body, but you could technically thicken the arms as there is the armour layer overlapping the arms after all.
The shoulders are actually a bit smaller than how they are portrayed in Metroid Prime (just google Metroid Prime in google images and you'll see), but not notably smaller so they are probably fine as is.
The shoulders are actually a bit smaller than how they are portrayed in Metroid Prime (just google Metroid Prime in google images and you'll see), but not notably smaller so they are probably fine as is.