Why are the bosses so large?

Why are the bosses so large? I understand that if its a mutated enemy, then it could have a huge size, but what about Darak? He was a giant even before mutating in the second phase. when we encountered him on the bridge, he was already a giant! This kind of logic is strange.
Does a boss always have to be huge? I wonder if we’ll encounter some human-sized bosses in the future, which could also make for great battles.
Other games like Nioh, Elden Ring, and Sekiro feature both large monster bosses and human-shaped bosses, which diversify the combat.
The way you designed Darak worries me because he should have been human-sized before mutating into a large monster.