How to win with a “weak” Knight?

However, by that time, the guild is usually well-established. There might even be a green Tower with a single unredeemed dragon. Fighting a beaver hero who has bought out the main armies in 2 weeks, even with dragons, is not easy. You need your own warlock hero who has visited at least a couple of gazebos. When the enemy army is reduced to at least 400 hit points, you can start fighting.

Yes, it's not easy. You can use standard methods to minimize losses: single archers to distract the enemy's strike force, single gargoyles to take out retaliatory attacks before the dragon strikes. The problem is obvious: if the computer has superior ranged power, it won't advance but will protect its archers. If it advanced, you could effectively use the speed difference between different units.
What can you realistically do with a dragon and some other troops against a barbarian if a knight hero attacks?
1. Take out the retaliatory attack and then continue attacking with dragons. This is where the advantage of building with archers that counter units with prolonged attacks (colored dragons, phoenixes, cyclops) comes into play.
2. Ideally, this attack should be timed so that in the second round after the attack on the dragon, it also takes out two units with its retaliatory attack.
3. Even weak magic from the knight can help protect the dragon. Slow, curse (if you're lucky, blind).
The main problems are the compact formation of archers, which leads to massive attacks on the flying unit, and the regeneration of trolls, as well as the large number of hit points of upgraded ogres. It might help if the barbarian, after his initial advance, goes to the left towards the village, takes it, and leaves part of his army there. If he goes to the right, towards us, there is also an option: he will take the intermediate Castle (on the way), leave part of his army there, and we will take him out piece by piece.
But what to do if he goes straight, I don't know. Theoretically, you should immediately rush to the top and take his Castle, and eliminate his hero with forces from the starting knight Castle. In practice, it's different: the forces from the starting knight Castle go to the necromancer, and there won't be enough gold for two fronts. Apparently, a chain is needed again to slip to the top and take the Castle, and then pass this dragon back to the exit from the isthmus, where another hero will be waiting (for example, the one who took the Castle on level 127 from the warlock). However, if the barbarian captures a couple of villages by this time, builds a Castle there, and breeds heroes, the game will drag on. Besides, you still have to chase him. A wizard could help here, but you can't really count on him.
However, more often than not, the barbarian goes to the left towards the village.