My big killer feature for Linux phones is running Wayland/X11 apps mostly unmodified, if AOSP added support for that I wouldn't be too disappointed about sticking with it. I've tried to make android apps before, but doing things the Android Way™ basically requires you to use java and their bespoke UI primitives, and it always makes me wish I could just use the tools I'm already used to.
Being able to have intricate control over my phone is nice, but I'd rather do it with a KDE-like settings maze than a terminal because of how tiny the screen is, and if I'm doing something serious that would require a terminal I would rather do it at my desk.
I definitely think the Android ecosystem has some serious problems, but I already run a custom ROM without Google Play Services installed so I'm fairly well-insulated from that. I do plan on installing a mobile Linux system on my old phone to experiment, but I doubt it will become my system of choice.
Godot's 3D is perfectly usable in my experience, it's been a while since I've used Unity though so I can't tell you how they compare.