Tactics for the Swamp (Fortress).

Tazar's army: 30 Lizards, 14 Flies, 46 Gnolls, 4 Wyverns, 8 Simple Basilisks, 2 Hydras.
Valeska's army: 56 Marksmen, 60 Pikemen, 12 Crusaders, 28 Griffins, 12 Centaurs.
No artifacts.

It seems to me that this is not a very accurate example.
1. 30 Lizards – 18 from the Castle and 4 from each of the three native heroes. Not bad.
But 56 Marksmen – 27 from the Castle and 29(!) from Valeska and two other heroes. So, Valeska has 3 stacks and two more heroes with an average of 6 archers each – that's optimistic. We're talking about SoD here...
2. 14 Flies... Why not 16, even if the heroes didn't have any? Okay, they were given to other heroes for speed. But where did the 28 Griffins come from if there are only 21 from the Castle, and we assume the heroes don't have any?
3. Why do you think the Castle built one more building?

This is how Valeska's advantage gradually built up in the endgame. And if we talk about hidden advantages, it always seemed to me that the Swamp has more of them on average, although I may be wrong.

P.S. Hmm, and by building Griffins instead of Centaurs, are you over-preparing to always have time to build the Castle, even if you don't have archers at the start, which is a big disadvantage for the Castle?
In TT, I would only play for the fact that it always has 2 levels.