In a tournament, with Necromancer heroes banned for the initial clearing of the map, people switched to Sanctuary mages with Kappa and Priestesses. They also clear the map quite well. :)

??? And what do the Kappa and Priestesses do? What's their CHEAT?

Added 5 minutes later

Yesterday, I tried a few starts in "Broken Alliance," and with eight Spectres, I could reach any gate and go, provoking everyone: both neutrals and heroes.

That's what the gentlemen mentioned earlier were talking about... I also tried this tactic. It's not difficult and it's effective. However, it's not very interesting to play this way, as you don't get to experience the full range of possibilities in the game, and you don't get to enjoy all the features and effects (Lich strikes, Weaver abilities, etc.).
Besides, you can play with this tactic for any faction. Because already in the first week, no matter which faction you play, even on a difficult level, you can buy 2 or even 3 Necromancers, and then easily pass any battle, building and rebuilding almost nothing.