#You don't have a problem

1. Your view that "physical strength and prowess don't matter in ranged combat with advanced weapons" is incorrect. They just don't matter in the same ways that they did when you just wanted to hack swords against each other. Sure they're not swinging swords, but they are doing a lot of running while carrying (sometimes heavy) weaponry.
2. Military training matters a lot, and if the girls are busy doing magic and magic related training, the boys have a lot more time to do military training.
3. Men are also more likely (due to testosterone and other factors) to want to fight, making them predisposed to want to do that kind of work.

You don't have a problem

1. Your view that "physical strength and prowess don't matter in ranged combat with advanced weapons" is incorrect. They just don't matter in the same ways that they did when you just wanted to hack swords against each other. Sure they're not swinging swords, but they are doing a lot of running while carrying (sometimes heavy) weaponry.
2. Military training matters a lot, and if the girls are busy doing magic and magic related training, the boys have a lot more time to do military training.
3. Men are also more likely (due to testosterone and other factors) to want to fight, making them predisposed to want to do that kind of work.