Saw this question posted elsewhere, so I'm paraphrasing somebody else, but the privacy benefits of Graphene OS are ESPECIALLY impactful if you're using invasive apps. The whole point of setting up all of the extra sandboxing, storage limits, network restrictions, yadda yadda yadda, is specifically for people who might need or want to still leverage some apps from bigger, less trusted providers.

I'll flip the question, if you're only using trusted, vetted, open source applications, do you even need GrapheneOS? Why not LineageOS, which also comes free of gapps?

And this also fully neglects the inherent distinction between privacy and security. Maybe you trust google knowing you called your mom last night, but you don't want your oppressive conservative government accessing your phone to view your Signal messages to your Grinder date. There's more to privacy than just the number of times your phone pings Google Telemetry servers.