My view on Shigurui vs Blade of the Immortal is that while Shigurui featured decapitations, horrific disfigurement, bisection, and boy rape, this is just fairly typical of the period.
Edgy kicks in when someone is, for example, murdering succubi and attaching their heads to his shoulders and then gloating about it. Generally edgy comes when it's trying to be cool about excessive violence, when it sticks a teenager's view of what is cool onto what is violence.
Shigurui handles it well - Violence is obscene in that show. But it happens.
Although watching the second episode of Blade of the Immortal, it becomes less edgy. Still doesn't handle violence as if it was horrible though.