Thanks for the review.
I think that’s the case for pretty much every custom ROM. Camera is an area where Sony’s smartphones have always been among the best performing devices, largely because of their experience with making digital camera, which they brought to their proprietary mobile phone software as well. It’s a key selling point for their own-brand devices, and they don’t like giving that advantage away.
I don’t use the camera a lot, and I’m not an expert, but it might be worth searching in some of the XDA Z5 Compact forums for discussions about camera quality. In particular look at the LineageOS Unofficial 17.1 ROM and Unofficial 18.1 ROM threads.
This unofficial build is based on the Unofficial 17.1 ROM, so it’s always worth looking in that forum if you need more information on a particular Z5c-related topic. There are more experts there than here 