Question: How would this magic “energy weapon” change medieval warfare and battle tactics (if at all)?
Answer: Indeed, even a concise bit of leeway is a favorable position. In pre-Revolution America, rifles were regularly used to shoot one volley to terrify and harm the adversary. At that point the assailants dropped them and accused of hand weapons.
In the event that you can occupy, immobilize, or shock your rivals, you’ll have the option to control the fight. Regardless of whether you can shoot your weapon at only 10% of the adversary, you’ll have the option to win a fight, every single other thing being equivalent.
Another bit of leeway would be focused on slaughtering. It seems like you could assemble a few fighters and target very much ensured foes. In the event that your reality utilizes customary battle strategies,
the foe administrators may be inside sight (yet out of bolt extend). Carry ready to slaughter them right off the bat in the fight could make for a short war.