"Weak demons"??

The Tower faction is only better at the very beginning, when you have Assassins and Furies. There is usually enough mana for one battle, if you don't constantly run back to the Castle or to the fountain. But a little later, when you have most of the units, Inferno is better, because the gates take the brunt of the attack, while the Tower usually loses at least someone in a normal battle, especially the Furies don't live long.
Archers are not a big problem compared to other factions. You divide all the mobs into 7 groups and open the gates, then cast the Curse on the archers. They will only have time to shoot once, then the gates will block them and they won't shoot anymore. But they often manage to shoot once even against other factions. So there are no more losses here either. It's more difficult with spellcasters, but Dryads hardly deal any damage. And dogs and horses reach the large archers on the first try, as well as the small ones, if you increase the speed by one with some boots of speed or use a tactic.