So, hardened armor and reinforced structure effectively reduce damage by 50% like reflective or reactive or ballistic-reinforced armor vs appropriate weapons? But instead of being merely multiplied by 0.5, it is treated a bit differently, being presented as absorption effect, presumably to retain fractions.
This makes hardened armor pretty good, previously it had uses but its drawbacks were pretty big deal. This adds further bonus to the armor, especially for heavier 'Mechs as they can't be knocked down as easily anymore.