I'm surprised to hear you say that. I've played the most demanding Android games on the Pixel 3a with no issues. I've never experienced anything but a butter smooth UI on Graphine or Lineage to be honest. The battery life has been all day for me even when using GBA emulators for multiple hours a day.
I agree the default camera app of Graphine isn't great, but it's picture quality better than the iPhone I came from (iPhone SE gen1)