Not sure how applicable this is to early medieval warfare, though — it’s one of my large collection of unpopular opinions that combat morale worked quite differently before the advent of pointy bullets, nitrocellulose propellants, high explosives, and the empty battlefield.
You’ll not find that opinion unpopular in this quarter. I’m firmly in the camp that holds that people thought very differently back then. That extends to how and why they waged war, and perhaps also to their willingness to put themselves in harm’s way, although it’s all a very complicated topic.
The shock effect of seeing/hearing something dramatic and outside one’s previous experience is surely not to be underestimated. Think of people in primitive societies, whether medieval or in C19 colonial conflicts, who may never have left their quiet village and never heard anything louder than a church bell/gong or a cow in labour – and confront them with explosions, rockets, massed drums or trumpets, disciplined ranks of redcoats … I reckon that would affect my morale.