Rather than throw his composite armor on full power again when he was already range for melee combat, Kuroda just took the shot, letting it too some decent damage to the armor in that spot and pushing through the pain as he swung to take out that bothersome rifle. Since he was by far more equipped for melee combat than ranged, he didn't really care if the red Gundam took out its katana, that probably putting him at more of an advantage than he had now. If the other pilot did choose to continue the fight with the sword, he would cut his boosters and put an average amount of power into his armor again, letting him fight without being too slow or too vulnerable.