Great to have GrapheneOS. We need alternatives. However, it only works with Pixel devices as of now, which make up a small part of the total android phones in use.

In general, all the alternative ROMs (lineageos, graphene etc) are not easy to install for standard user and some have limitations (e.g. open bootloader means some apps won't run). Adoption will only grow if it gets easier to change OS and keep app compatibility.

I'm currently using lineageos with microg, which is as good as it probably gets for a de-googled experience on a non-pixel phone, but not perfect.