Tactics for the Swamp (Fortress).

In my opinion, it would be more reasonable to ask: Why do some people dislike the Swamp faction?". After all, all factions have their pros and cons. I have a neutral attitude towards them.
+Mine, in any case: hero Bron.
+Transition from Snakefly to Wyvern.
-Creatures are relatively weak.
-Magic is poorly developed.

This is just an opinion, don't kick me.

Well, Tazar will be stronger than Bron.
I didn't understand about the transition. Wyverns are built after the Lizard Pit is constructed, that is, at most on the second turn, if there are enough resources. The creatures may not fight very well, but they are quite initiative, and thanks to the hero, they have high defense.
The third level of the guild is enough for a start. All you need is slow, haste, dispel, shield, stone skin, blind. Perhaps not the best set of spells, but it suits me. And then you can capture a secondary or even an enemy castle, which is much easier to do with wyverns, and then build a stronger guild there.