Olivia is meant to be more than just a healer. Basically, by the game's end, Olivia pretty much is supposed to be the Hero of the story.
Her skills are supposed to constantly be improving both attack, defense, and healing.
What the MC's done is interfere in battles Olivia was meant to solve on her own.
Think about RPG games. The area with the dungeon was supposed to be the early place for Olivia to grind and level up. Well, MC over here decides to tag along and kills most of the enemies for her.
It limits her growth by alot by having a stronger person to rely on whose taking the lead and doing most of the heavy lifting. It doesn't teach her to be stronger and independent, it teaches her to be a sidekick.
She doesn't learn responsibility, opting to just follow MC around everywhere and let him call the shots. She's not supposed to do that. She is supposed to be the one making decisions, SHE is the original main character.