Fungal Growth Tooltip: "Seed a large area of mushrooms that heals you and all allies in your frontal cone for Health."
The tooltip seems misleading in calling the area of mushrooms "large" because the width of the cone is quite small, which requires precise aim from the user that increases in difficulty as common variables become present in battle (such as ally movement and healer movement). Due to the size of its cone, Fungal Growth has a smaller margin of error compared to most other heals in the game, which are heals that offer a larger margin for error and are more capable of handling unpredictable movements of mobile allies.
The higher rate of missed heals coupled with its casting cost makes Fungal Growth difficult to consider using over (for example) Grand Healing, which is a targeted, wider AOE heal that offers a larger margin of error, hits multiple targets, and has a cheaper cost.