The Kignsguard guarded the King or their assigned ward in battles and duels, this is already done still for the battlefield duels so leading armies will still be good.Because they traditionally lead the armies of the Iron Thrones and accompany the royal family members who do lead them. Makes no sense have an elite bodyguard that can't fight with the monarchy in battle. Just a thought I had. The commander system seems to misplace what the King's Guard do traditionally.