I have an idea. We have a tower. We have plentiful metal.
Make a lightning rod.
And yeah, we do not have any anti-magic capability AT ALL. The 'anti-magic charms' basically only work as crappy alarms, they don't do anything to stop enemy magic. That's why I voted for them to be revised. We have a lot of half-finished spells and projects in our arsenal (the tower of Forever Frost that does jack-shit in helping us, the anti-magic charms that aren't anti at all, crystal axes that are too expensive to be worth it, magic lances that are also expensive, etc.) The plate armour, fireballs and anti-wizard guard appear to be our only useful weapons. I'd argue that barring Moskerg unveiling some magical superweapon next turn, we should spend the next design phase on improving something again, like we did with the fireballs this turn.
Oh, and cheaper longbows won't do much good. By all measures we should already be beating Mossberg soldiers in physical battle excluding the use of magic: we have plate armour that renders (a third of) us invulnerable to arrows, longbows that outrange the enemy's, crystal axes for our officers and crystal lances for our cavalry that are quantitatively equal and qualitatively superior. The problem isn't that we're getting beaten by Muskergites in physical combat, but that we're not getting to do so with Muskberg magical interference before the combat, in the form of weather control and sleep spells allowing them to get the drop on us.