I think it is useful to use fdroid in conjunction with private OS like graphene, divest and calyx all with excellent android compatibilities. Unfortunately, grapheneos, IMO the best of the three, is only avaliable on a small set of devices, like iPhone.

But I do agree with your point, if you use the stock OS, even with privacy hardening, it is probably still not so private. But I don’t know if a hardened stock android is “worse” than an average user’s iPhone.