Tactical retreat.

Yeah... good thing I don't really like the Faceless Ones. There's a reason for that. This isn't an imbalance, but a racial trait.

It's still an imbalance, although it's a very annoying one. Order already has strong and versatile magic, and warriors that, by the way, are suitable for almost all Castles... And then there's something like: "Cut down half the army and run away without paying and without losing troops," which gives a big advantage, especially when defending. Of course, you can upgrade this spell for other factions, but you have to spend levels and find the spell, which isn't always easy. Although, they shouldn't have made "Portal to Town" level 4 for the Faceless Ones; they removed the useful property, but increasing the spell level... is too much, although it's good that they lowered Blindness to level 3. In the end, you get: Ice Bolt, Forgetfulness, Blindness, Berserk (general slow), Phantom, and Hypnosis, and you'll have to struggle against Order.
P.S. Adding to the tactical retreat options - to some extent, "Portal to Town" can be replaced by a combination of armored heroes, a mage, and a warrior (or two mages), since the heroes can freely run back to the Castle (it would be even better if they didn't lose a turn doing so). Such a pair can severely thin out the enemy army, targeting units rather than heroes. Hit them and run back to the Castle, tactical running around:D