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The rules can be agreed upon in advance, but by default, I don't see anything wrong with it: real wars often have several fronts, and no one is bothered by this; it's just another way to demonstrate one's gaming skills. Instead of fighting head-on, use all available resources and, if possible, several heroes: after all, this is a strategy game, not some online RPG (which the Heroes series is slowly but surely turning into, as seen in parts like the sixth). I won't even mention that in the fifth game, some factions (Warlock) have little chance without hit-and-run tactics, which you also "condemn."
But against a normal player, one mistake by the Warlock, and the game is over. And that's also a waste of time.
On the other hand, following your logic, you could also agree on "not rebuilding" fortresses, right? :))))))))))
I don't argue, but the fifth game wasn't designed for those who want to play a lot of games quickly and increase their rating: it's for those who can be patient and enjoy the game. Unlike the trends I've noticed in the sixth part.
Multiplayer is primarily about time. Many of us are adults. I, for example, have a family, two children, and a stressful job. The fifth game was a kind of escape: dynamic and almost balanced.
Rebuilding castles saves time in multiplayer while maintaining equal chances for players. The same applies to mines and dwellings. If they had kept simultaneous turns, it would have been the ideal multiplayer experience among all the "Heroes" games. But for now... we're waiting for the add-on.