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After switching to SSR mode I was able to better debug, I figured that the beforeCreate hook is called after the layout is mounted after switching to SSR which I should have realized after seeing this image on the nuxt documentation. So I realized the isAuth state getter was being checked before the authentication happening in the beforeCreate where I was supposed to be checking the sessionStorage.
https://nuxtjs.org/guide/views
Also found this to help out authentication using middleware.
I solved my problem but am still insecure about my design patterns so still open to criticism and please correct me if there is anything wrong with my answer!
EDIT
I found an example which really helped me out, if anyone else is struggling with authentication with firebase and nuxt check out the following example by davidroyer.