> /e/ OS with Fairphone is the good choice for that.

That's debatable. /e/OS is mostly made of AOSP, which is made by Google.

> It is less secure than Graphene

Most definitely, yes

> but also leaks less data to advertising companies.

This is wrong. If you don't use microg on /e/OS or Play Services on GrapheneOS, then it's equivalent. If you use microg, it still contacts the Google servers even though it is an open source reverse-engineered implementation of Play Services. The added privacy there is to go through a proxy, which GrapheneOS offers.

I actually like it better to run sandboxed Play Services through the GrapheneOS proxy, because in my experience it works a lot better than microg.

Really, the only reason to use LineageOS or /e/OS (which are interesting project, really) is that you cannot run GrapheneOS on your phone. If you have the possibility to use GrapheneOS, there is no good reason not to do it.