I'm not sure why anyone would expect perfect accuracy when making a replica of an non-existent and completely absurd weapon for fun. That it was bigger only makes it more awesome, not less.

I noticed the flex in the blade too, but I can't fault him for not hardening it some more when it's clearly ridiculous. I wonder if it would become too brittle under it's own weight if it were hardened. The thing couldn't have been light.