I guess? But Linux provides those things. Break it apart, what this is saying is, "you don't want X, you want something that doesn't exist that theoretically provides all of the advantages of X."
Which, sure. I could (and do) use LineageOS right now. It's not as good. I still need to go through the Android app development process, I'm still fighting the system every step of the way. It's still a pain to de-Google things, I still have to deal with an architecture that if fundamentally designed to work best with Google services. I still have to deal with what I see as design flaws in Android itself.
So I don't technically need this to be Linux. I recently bought a smartwatch that runs on an ESP32 chip and is programmed using Arduino code/C++. It's not running Linux, but it fits a lot of my needs and it will communicate well with my Linux computer. And you're right, I didn't have serious qualms about that because of the kernel. In fact, the simpler dev process was what made it attractive.
However, there isn't that kind of thing for phones. If you want an Open Source phone that is easy to modify and develop on, Linux is the option that's pushing in that direction.
> but they don't necessarily want to open a PR against the camera app if they want it to more closely match the polish of iOS.
It's deeper than that: I want the ability to fix my own problems. I don't want to open a pull request, I want software that is understandable enough and an ecosystem that is open enough and broad enough that it is reasonable for me to fix my own problems. I (personally) can do that on Linux, but I can't (currently) do it on Android devices, they're a pain to work with and I hate them.
I am used to Linux on my computers, including the fragmentation of software. Sometimes the fragmentation is an advantage because it means there's a diversity of software that is hyper-specialized rather than one or two solutions that are built to kind-of satisfy "most" people's needs. More than Linux itself, what I am used to is the idea that if something goes wrong or if I want my computer to do something, I can make it happen without asking anybody else's permission, without building a giant project that I need to invest serious time into, that I can pull things apart and build pipelines with Unixy tools.
I want that on my phone. It doesn't have to be Linux, but nothing else is providing it, so it does have to be Linux unless someone else is going to build a better OS. I'm not holding my breath for that.