/e/ includes microG per default and thus calls google servers. /e/ includes unique identifyer per update call tracking its users. Graphene uses several proxy servers to hide user information, /e/ does not in similar way. And so on…
They use Graphene. That’s the point. Pixels are unfortunately the only supported devices. That’s why I won’t use Graphene as I would never support google. A pity, many do
Using the promoted /e/ results in loss of support (you habe to flash back FairphoneOS). Maybe this has changed as they are sellig phones with preinstalled /e/ by themselves
/e/ is very slow in terms of security updates and they rely on some google services.
The only point you can make: If you want it easy and you don’t care about security and less google but not degoogled is okay for you, /e/ is your choice.
But please stay away from Fairphone. They have several hardware issues even in more than one generation (for example ghost inputs in 3 and 4) but they do not accept them and try to solve with software update which surprisingly did not work. And if you use /e/ you don’t geht support from FP side.
Fairphone is known to have several hardware related problems, but they usually ignore or do not acknowledge them. Recently they tried to argue a hardware problem (ghost inputs) can be solved via firmware update, but of course it couldn’t. Additionally you lose support for device when using custom roms (even /e/os). They only support google Android. You could buy from Murena but they can not help with hardware or firmware issues. Fairphone is very to patch their devices in terms of security.
But google is google. I would never give them money.