One word: Duh.
When Zack Fair talks to his mentor about the Buster Sword, he comments on how pointlessly heavy it is, and the mentor comments on how he carries it so as to not use it as some sort of philosophical message. Mostly, he treats it like a back weight. Also note that Shinra SOLDIERs are Mako-infused, making them as strong as Master Chief physically, at least at first. You know how magic gets. So yeah, obtain magic glowing steroids, then come back and try again.
When Zack Fair talks to his mentor about the Buster Sword, he comments on how pointlessly heavy it is, and the mentor comments on how he carries it so as to not use it as some sort of philosophical message. Mostly, he treats it like a back weight. Also note that Shinra SOLDIERs are Mako-infused, making them as strong as Master Chief physically, at least at first. You know how magic gets. So yeah, obtain magic glowing steroids, then come back and try again.