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In two weeks, even without focusing on Archdevils, you'll already have a two-week-old army from your Castle, plus Wyverns and Angels, and a somewhat leveled-up hero, along with explored territory, possibly even a second Castle. But if you focus on economy, your army will only start appearing, your hero will only start leveling up, and the territory will only be explored if you're lucky with the paths.
To be honest, I used to play focusing on economy, but now I'm learning to develop my army because it's more challenging, interesting, and rewarding. ^_^
Especially on random maps.