*secretly* The fact that the damage numbers in the tooltip don't increase with the attack range doesn't necessarily mean that the horses are bugged and deal damage without retaliation. How about three consecutive turns of horses (and with waiting – all four)?
Of course, the AI doesn't place guardians properly. It's interesting to see what your camping tactics will lead to when playing against a human, who will wipe out your stack of archers.
As for the human player, that's just circumstantial. But we're talking about the campaign and computer opponents.
The damage of ONE stack of archers is definitely less than the damage of FIVE stacks of melee units. I've said everything, there's nothing more to add.
Closing in and camping is not interesting at all...
As for the interest, that's beside the point. How interesting it is for you to dominate the AI is your personal business; I'm just describing a perfectly viable and simple tactic.
And abilities don't matter much for good players.
You can defeat archers with griffins just as well as with ballistae.
Regarding tactics, I was talking to a friend today, and he reminded me that I'm slow... I, despite emphasizing knights, completely forgot about their ability to move through obstacles (including castle gates). I don't remember if they get this upgrade on this map, though. In any case, reinforce them and go break down the gates and everything behind them.
But you can also resurrect them and Vestals in the castle O_O (I used to build a different structure, but now I noticed).
After defeating the barons and capturing all the alliance's cities, you don't need to rush anywhere.

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!