I described my point of view; I like to play with one hero. It’s just more convenient for me. Of course, the hero must be good. If the hero is strong, then a large army theoretically makes the situation worse (I mean a large army that isn’t strong, but consists of many weak creatures). I’ll explain: let’s say in a battle, my enemy consists of griffins. My hero knows 5th-level Chaos magic and 1st-level Warfare (making the hero level 21). It will be easier for me to defeat the griffins with one hero than, say, with berserkers, centaurs, and thieves. First, it takes longer. Second, the enemy army will be divided into three squads in battle (because of my army). But if the hero is alone, there will be one squad of the enemy army. And it’s easier and faster for me to defeat one squad than several.

This isn’t a very convincing justification for your point of view. Two heroes are definitely better than one that is only slightly stronger than the other two. You can combine tactics in battle with two, and there are many such combinations. Dividing the enemy into small squads is also useful. Examples:
1. Two Chaos heroes with a small force to divide the enemy squads. We choose a location where only one squad can attack us. One Chaos hero covers the other, having drunk a potion of healing beforehand. The squad attacks him – he gets up. Then, the magic that skips the enemy’s turn is constantly cast on this squad. The second one sprays everyone with a flamethrower. If the enemy doesn’t have archers or magical units, you can defeat solid troops in this way, and we’re not talking about heroes of level 15, 18, or 21, but much weaker ones – like levels 5-10. The question is only about the number of mana potions you drink. :)
2. Let’s say a Barbarian and a Life hero. The same thing. The Barbarian covers the Life hero, and he casts, for example, regeneration, shield, retribution, and periodically heals. The Barbarian can simply press the “defense” button if he’s having trouble taking the hits. But when the enemy in the squad is reduced, he will restore his health with regeneration and is ready to receive the next enemy squad that attacks him. Here, too, I meant not very powerful heroes.