They don't tell you the rest of the raid composition in OP, i.e. who they were competing against. If you had a raid that was melee dps heavy then I could understand them swapping out the Shadow for a ranged (Sage) ahead of another melee DPS class with better utility.
Like I said, it's unlikely that his presence determines the fails by itself, unless is messing up something badly. If he's doing 2nd overall dps in the raid, unless he pulled aggro and made the boss cleave the raid multiple times, the problem doesn't lie there.
Like he said, they finished the raid because they used a sage for the offheals. You know what this means? The problem lies in the healers most probably.