Almost everything you said here is false, with the exception of controversy over the developer. However, GrapeheneOS is far from a single developer project, and the former lead stepped down a little while ago.

I have a 6a, which I tolerate for GrapheneOS. The battery life is absolutely terrible.

Just convenience in the form of focusing on a user-friendly out of the box experience, really. That’s enough for me to use it over Debian on desktop, though I like Debian for servers.

It would be nice if they fixed their app so that when I set it to always dark mode, it actually stays in always dark mode. I don’t have much faith in UI improvements when that bug has plagued me for literally years, across Android versions and devices. But now the colors that suddenly blind me when it changes from dark to light will be different, yay?

Speak for yourself, I’ve been prepared to submit detailed bug reports before the process in place to do so turned me off.