Because their faith in the Emperor is so strong it allows them to perform literal miracles, and even caused one of their members to become so powerful she is now for all intents and purposes a Daemon fueled by devotion to the Emperor rather than devotion to Chaos.

So it is less a case of "We used extreme biological science to create ascended men who are so ascended it is arguable they arent even human anymore" and more "I believe that I can stop these bullets, and my faith is so strong I literally manifest a force field that stops the bullet".

Because their faith in the Emperor is so strong it allows them to perform literal miracles, and even caused one of their members to become so powerful she is now for all intents and purposes a Daemon fueled by devotion to the Emperor rather than devotion to Chaos.

So it is less a case of "We used extreme biological science to great ascended men who are so ascended it is arguable they arent even human anymore" and more "I believe that I can stop these bullets, and my faith is so strong I literally manifest a force field that stops the bullet".