The tactic you described for playing as the Swamp faction is interesting. I usually play at 200%. And on average, I build: 1st week: a Prefecture, Wyvern, Citadel, Lizardmen, and 2 heroes. I buy Lizardmen and Gnolls.
2nd week: Either I finish building up to Hydras with a Castle, or I build a Capitol but without Hydras (if I don't have enough sulfur).
By the third week, everything is built.
Usually, I buy Lizardmen and Gnolls and storm Necropolises and capture treasure chests in the first week.
In the second week, depending on the circumstances, Wyverns usually join.
But I can't seem to build so quickly! What's the mistake?