the concern is not code written by google, but code that depends on googles infrastructure, requires a google account, phones home, gives google control over my phone, is not released under a FOSS license (so i can't change it), anything that violates the users privacy...
so what /e/ is doing is essentially an audit of android, and an attempt to remove everything that is of concern.
it's a major project, and it's not complete. work in progress.