A quick clarification. If you are using FSR, it's not rendering natively. That's pretty much the point to improve the performance. Unfortunately FSR is not magic.
To be honest without a "Digital Foundry" like comparison with native vs FSR modes which would differ for still images and in motion. Everyone is going to have a subjective opinion on it. I would expect native resolution to always look better than FSR in its current implementation.
From most of the FSR comparison videos online, very few recommend using FSR or DLSS if you are running a 1080p screen.
Have a look at something like;
Source: https://www.youtube.com/watch?v=zDJxBykV1C0