Tactics for the Stronghold.

Apparently, yes, there's no other way.
In that case, you should take Dessa, but I usually took Kreg or Gundula. Maybe that's why I kept losing.

You know, I experimented: I took Dessa and... I still lost.
Moreover, the situation was completely idiotic: we recently played a two-player game on a Small map. I was playing as Stronghold with Dessa, and my opponent was playing as Rampart with Ivor. The map turned out to be structured as follows: in the upper half, there are 2 Strongholds (mine and a neutral one), and in the lower half, there are two Ramparts, one belonging to the opponent and the other neutral.

The development followed the previously discussed scheme: in the first week, I built a Monster Lair (I had to sell 42 Goblins into "slavery" and lose 2 Rukh in a battle for the Crystals), and with two Monsters, I cleared a path to the second castle, which was also a Stronghold. I quickly explored the surrounding areas (the second hero also gained logistics thanks to the Stone of Knowledge) and reached the border of Crulod and Avl, defeated those guarding the passage, and infiltrated the enemy territory. I reached the neutral Rampart and captured it. So, in the end, I had 2 Strongholds and 1 Rampart, with a total income of $6000 per day.
Just then, Ivor appeared around the corner. Seeing Dessa, he immediately requested reinforcements, and his army was filled with Dendroids and Gnomes, and there were also 3 Angels.
Realizing that the situation was unfavorable, Dessa rushed home, leaving the Rampart to its fate... I bought out all the Centaurs and Gnomes there (they shouldn't fall into the enemy's hands), looked at the size of the enemy army - about 50 Grand Elves, 3 Archangels, 8 Great Unicorns, 8 Guardian Dendroids, 160 Centaurs, 32 Silver Pegasi, and 60 Gnomes...

In order not to waste time and delay the inevitable, I proposed a meeting with the enemy on neutral territory. I bought out everyone I could, transferred them to Dessa, and went into battle...
In total, there were: 7 Monsters, 26 Rukh, about 20 Ogres, 54 Orcs, 80 Wolf Riders, and 220 Goblins.

The battle didn't go well from the start: among the good spells, I only had Forgetfulness, and even that was at a normal level. With the first move, the opponent cast Mass Slow, and my Goblins became disheartened - with that speed, they definitely wouldn't reach the enemy... even the movement speed of our "walking excavators," the Monsters, was reduced to 3. Casting Forgetfulness was already pointless.
The few Ogres (there were problems with wood) couldn't protect the Orcs from the Pegasi, and the Unicorns that arrived quickly destroyed both of them.
The Elves shot down the Monsters as they approached, and the Gnomes and Centaurs easily stopped my horde of Goblins.

In general, it turned out that even though I had troops from 2 identical Castles and was holding one of the opponent's cities, the Stronghold still lost.
In general, among the factors that influenced the outcome, I can highlight:
- the opponent having expert Earth magic;
- the presence of external dwellings for creatures (level 1 and 2);

In general, I don't even know what conclusions to draw other than that you need a lot of luck. Maybe the tactic of building a Monster Lair in the first week is not what you need to win?