The module starts at level 1, so with some healing, getting to level 2 could happen within a few short encounters. They might even be level 3 before they fight cyanwrath.
I must have been thinking of a level 3 party fighting Cyanwrath. My same basic point applies: the XP curve is very steep from levels 1-6, so you won't be much ahead of the level curve by having 33% extra XP (and you need to survive those early encounters to do so, extra healing potions aren't always a good substitute for another party member).
E.g., what would you rather have: 6 PCs with 300 XP (level 2)? Or 2 PCs with 900 XP (level 3)?