It sounds like you're suggesting Linux phones are more private and secure than GrapheneOS. Given their current state and limitations, it is extremely unlikely that any of them are more secure than GrapheneOS against a typical hacker or malicious app.

with the downside that is limited to one single phone brand

In terms of security, this is also a benefit. It means they aren't trying to aim at fifty different targets which may behave different or even unexpectedly. The software developers have far far far more confidence that their security features will work on your device if they test it on theirs.

Again, there is no such thing as “full privacy and security”. It is unpragmatic idealism. Not only does it misinterpret privacy and security as concepts, it is an unconstructive attitude for creating an effective security model, and just encourages burnout for no benefit. We don't limit "full". There is no full. There is no perfect answer. It's an undefined and unachievable idea.

"[Someone made] a laptop, encased in foam in a full Faraday cage, wrapped by alternating metal foils, and finally covered by a 1" layer of reinforced concrete."

"It had been billed as the most secure computer ever. Right until two research papers had come out that showed it was possible to decipher processing by the amount of power being consumed and by pulling the slight RF signal being carried by the ground line. "

Now, I'm not saying you can't effectively secure your device adequately against big-tech and corporate capitalism. I say you can! It's achievable. But it's unconstructive to hold the illusion that there is some absolute "full privacy" against them.