and a very significant portion of the Android ecosystem requires GPS to function

Which ones? Not encountered that except for maps.

Auto updates, built-in Android security features

At least Graphene does auto-updates of the system and basic apps just fine, and when it comes to installed apps - you can use F-Droid, Obtainium and other methods that can do it as well.

a significant portion of secure apps like banking and financial service applications

Yeah, those are often blocked off indeed. Although this depends too - for example, in my country all the major banks aside from one don’t require Google services, primarily to accommodate Huawei and other Chinaphones that come without Google services. Find My Phone - indeed, although there might still be workarounds, just not looked at that.

And it’s funny because each one of these removed features are generally replaced with a third party alternative, which means you’re still trusting a third party with your data…

Thing is - you have CHOICE in what third party to trust. And a lot of such choices are indeed more trustworthy than Google judging by prior history. You can eliminate middlemen, such as getting apps directly from the devs’ repos rather than from F-Droid. Oftentimes you can avoid a third-party entirely, as a lot of things are selfhostable.

You may be completely happy with Graphene, but the overwhelming vast majority of people won’t be because it removes the specific advantages of using Android as an ecosystem.

That’s not the same argument as you made previously - “De-googled projects get none of the benefit of being android, while all of the downfall of being android”. Removing Google does still leave a convenient daily driver - whether it’s suitable universally is another question.