"Has to inherit from MonoBehaviour so we can use Instantiate()" - wrong

[andypoly]

The code comment is wrong. You can make a reusable GameObject pool without monobehaviour because you can call Object.Instantiate - you just have to pass a prefab GameObject to it on creation. But that could be in a parent class or a pool manager monobehaviour.

[Habrador]

Thank you for your feedback - Ive added it as a comment!