Centaurs are quite decent archers. And in melee combat... In the early stages, they are very useful for a Barbarian. Especially if the hero has a Sniper's crossbow, which, by the way, is quite common. Although, of course, from the very first encounters with neutrals, they are just cannon fodder that distracts from the hero.

I agree with you, Centaurs simply distract the enemy from the hero. But they still have some use. Especially if the hero has an Elven King's Bow (plus one more attack in ranged combat for all creatures). I once experimented in the editor and created a Barbarian hero with full combat skills, with a Sword of Swiftness. I gave him a Potion of Swiftness, knowledge of Chaos magic, and an Elven King's Bow. And I added a Gargantua to his army. The enemy was a monster. During the battle, the hero drank the potion, cast "Cat's Agility" on himself and the Gargantua. Then they became very useful. In melee combat, the Hero attacked five times, and the Gargantua fired four times. That's some serious power, a useful team.