Well, with a commander, it's a rather large army. It also needs to be teleported, and the cost of magical energy will be somewhat higher than for 1 cart of ore or crystals per day.
Okay, okay, let's assume that. Let's consider this situation. An army runs into a cave and, waving iron and special effects, yelling, shouts to the local miners, "Hey guys, now you work for us," and leaves their regular mage from DHL, who will handle deliveries, while they run off to capture more mobile units. Apparently, this mediocre mage is so cool that the brigade of miners, who work day and night in inhumane conditions with physically demanding work, put down bricks the size of the Kremlin and obediently continued their endless work. BUT, another first-level hero, who has just started to grow a mustache, arrives with a drunken peasant. He gives this mage a good beating, who, damn it, can teleport heavy cargo (he could have teleported stones onto their heads). And leaves his own mage (yes, that is, each hero carries a bunch of mages with him... where do they hide when the battle is raging?). Something doesn't quite add up. I'm voting for forts; it sounds more convincing.
For example, the Orcs have a cheat totem for 250 gold for ANY battle, built in every city.
Well, this area is cleared in 2-3 days...
Also, I clarified that I'm playing on medium maps for two players, and there are only two cities on the map...
But in the conditions of the same 3rd game, if you had 1 mine of each resource and thus a decent amount of gold, it didn't really help when you lost 1 of the mines, especially if it was the "main" resource needed to build high-level creatures.