Even if you run a meatgrinder you still need a backstory (assuming backstory is relevant to the campaign). Unless you are all identical clones with identical training each potential PC still has individual skills, abilities and personality traits that are explained by their backstory before they entered the meatgrinder. So all the meatgrinder does is create a shared experience for the characters.

Where I see a meatrginder being possibly kind-of useful is where you run 2 or 3 sessions to introduce the players to the setting and ruleset and then use the surviving PCs as NPCs for the main campaign which starts after the meatgrinder.q