I've got the same guide - it doesn't take equipment bonuses into account, nor does it take into account ultimate weapons or power leveling. Basically, it's for the "standard and direct route through the main game", to quote the guide's text next to the graphs (opposite page). Vanille has a staff that enables her to get 20% extra out of her healing, so it gives it a pretty big boost - enough, I'd say, to outdo Hope.

Hope and Sahz are also debatable over who is the better Synergist depending on what angle you're wanting in your battle. Hope, with the right weapon, can increase the duration of defensive buffs such as Protect and Shell by 80%. Sahz, meanwhile, puts the same 80% onto offensive buffs such as Enfrost (again, with the right weapon).