A few things to remember about the camera on the 3a:
1. There's no Visual Core, so all of the photo processing is done by the main CPU. This means the processing will take longer for each shot, and probably will bog the phone down if you're taking a lot of pictures in succession.
2. Since the CPU is doing all of the work, this will also probably increase overall battery usage if you're taking lots of pictures, so any improvement in battery size over the flagship 3 would be offset.
3. From what I've seen everywhere, you won't get unlimited Original Quality photo storage on Google Photos -- only High Quality (which is still fine, but if you're a real photo enthusiast, you'll probably want the Original Quality).
4. Overall performance for the phone sounds very midrange, so you'd have to be prepared for somewhat sluggish app opening/switching, etc.
I think all those things are a fair trade off for a phone that is half the price of the Pixel 3 and 3 XL.