Theoretically, 1 Minotaur can defeat 1 Black Dragon, but in reality, it can't.
Let's say its block chance is 100%. During the Black Dragon's attack, the Minotaur will block. But does the Minotaur have to attack? Yes, it does. When the Black Dragon attacks, it will deal damage in return, and the Minotaur's corpse will lie on the ground for a long time.
Second scenario. Again, 100% block chance. The Minotaur will skip its turn and block the Black Dragon's attacks. This won't last long. Sooner or later, the Black Dragon's morale (Fervor) will increase. And it will attack twice in a row. And again, the Minotaur's body will lie on the ground for a long time.)))
BUT this doesn't follow from your reasoning. :))
The Minotaur blocks any NON-magical attack, and it doesn't matter if it blocks the counterattack after its own attack, blocks the first attack against it in a turn, or the 10th. Therefore, a Minotaur with 100% block chance is invulnerable to ordinary, non-magical units.))
But yes, theoretically, a Minotaur defeating a Black Dragon is possible, but it is very unlikely in practice. Although, I have had cases where a Minotaur blocked up to 6 attacks in a row! but unfortunately, it was a neutral one, not mine:(
Added after 3 minutes
It's hard to argue with that. Yes, Vampires are very strong, especially in Might and Magic IV (the strongest creature of level 3). They are especially useful in a prolonged war (although they are also useful in a quick one). If you have about fifty Vampires in your army, you have nothing to fear. But still, I would choose 15 Dark Champions over 50 Vampires. They have regeneration and the ability to cast the "Terror" spell. All of this makes them more useful than Vampires. Their usefulness lies in many factors that allow them to win in almost any situation. But unfortunately, the Champions' Refuge cannot be built in a city. Otherwise, they would be ideal warriors and share third place in strength with Sea Serpents.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!