The benefit of not relying at all on android code? Well, that would be not having to constantly adjust to what happens in the android code base. If google introduce proprietary code that the os depend on, one would have to create substitutions for that.
But with PinePhone and running e.g. postmarketos, then it's more pure linux and not have to relate to android and google's whims.
But I must say I AM happy with /e/os as a free degoogled android os. But it will still never be as good (or better) than "the real thing". At least that is my main concern
I run /e/os (linageos fork kind of) on my Fairphone 3. It works pretty good. At least I got rid of the feeling that google os watching me. I have no google software on it. I try to use as much FOSS software from F-Droid.
I use Aurora Store for those apps that are closed source and I need. (E.g. the swedish app Bank ID which handles auth and sign for logging into banks and authorities).
Hackerwise I would like to try out PinePhone but as I understand it, it is not really for daily use yet. But I like the kill switches and that it doesn't rely at all on android code base