Google Drive is great for writing unversioned content that you don't need to deliver elsewhere and/or manipulate programmatically; I use it myself a lot for this kind of tasks. But if you want your content to end up automatically online or in another application, if you want to keep full control of how it's displayed easily, and if you want to track and plan changes in an advanced way, then it's for sure not the right tool, and prismic.io sounds more like it.