Secure can mean very different things in different contexts. It depends on your security model.
Graphene only supports devices with:
hardware-backed keystores, verified boot, attestation and various hardware-based exploit mitigations
I won't use GrapheneOS. This video basically explains why: https://www.youtube.com/watch?v=4To-F6W1NT0
I use my stock ROM and followed the steps from this guide, with some changes like using Shizuku and App Ops, instead of AppOpsX: https://lemmy.ml/post/128667
Interesting, I went the other way around. I started with a similar setup as is discussed in the post before switching to Graphene. Google has Android setup in such a way it allows it them to navigate around restrictions established on the device. I wanted to install a privacy focused ROM so I would truly have control over what information Google can access, as it can be fully sandboxed with Graphene. Does suck to see the founder of Graphene is kind of a dick. Not to sure if this reduces the privacy and security Graphene provides, what do you make of Louis Rossmann's video? Seems to me as if he swapped his ROM due to customer service issues and not the code.
I can confirm that when I restrict Google apps, including play services, it works. For example, if I block internet access for Google Play Services, I can't receive GCM notifications anymore. Beyond that, if there is some other backdoor that goes around my VPN and restrictions, there isn't much I can do about that.
My opinion on the video is that I don't trust the code of someone that is that unstable. If I were to go with a custom ROM, I'd probably go for LineageOS.
If your concern is solely with Daniel Micay's behaviour he has in fact stepped down from the project as can bee seen in the following Nitter link provided. Otherwise I think debloating a stock rom is a good option for many people!
I find the yes the dev is a little intense, but you would be also when you have had multiple people harassing you and your project even going as far as getting squatted. The dev has a right to be mad, just because he's being hyper defensive currently isn't any reason for me not to continue to use GOS
