To a great extent, this effect is brought about by the artistic appearance.
A group of handsome armored men can stabilize the morale of the entire army. Their silent and resolute fighting can make allies, who would otherwise collapse, willingly stay and follow orders, gritting their teeth to hold on.
At the same time, the beautiful and uniform armor brings a huge morale boost to the Interstellar Warriors themselves, which is more useful than any flag or language. Among the collective, this unparalleled courage and cohesion empower them to challenge otherwise impossible targets, leading to a qualitative improvement in the army's combat effectiveness.
Moreover, in this era, those 'decorations' symbolizing human will, common understanding, and pure faith in The Emperor are not merely appearances. As long as their origins are correct, they can indeed help the Interstellar Warriors resist damage, strengthen their power, and even improve their luck.
