The weakest castle in Heroes of Might and Magic IV!

I didn't understand your logic!
so who is worse off against whom.

If a Barbarian has maxed out all combat skills (Magic Resistance 100% + Archery, etc.), then taking down this hero is very difficult. (A large army + Dispel Magic are needed so the Barbarian doesn't have regeneration)
But.... the army has no chance. Therefore, the Barbarian is stronger here.
If the Barbarian hasn't maxed everything out—for example, under-leveled Magic Resistance—then there is a chance to use Hand of Death. To prevent the heroes from being wiped out, the army covers them. The second hero casts Dispel Magic, and the main one casts Hand of Death. If it doesn't work, the Barbarian must still drink a "Potion of Immortality". Soon, Hand of Death will show what it is capable of. It is advisable to buy more "Wizard's Potions" as well.
In this situation, the Barbarian lost.