It feels like there's also more happening than just the resolution being lower, like look at the red particles from the blight, drastically different. Feels like holograms are also noticeable lower quality when in performance mode
Anything or effect that is resolution-bound would suffer or moe specifically... be different based on your resolution. So basically anything that is done in post-processing (PP) which is resolution bound. DOF, Particles, Motion Blur, AA, SSR....etc. Going from rendering ~8M native pixels to around ~3M with 180p CB, thats why you see so much of a cutback with any f the above-named features.
The issue with the 60fps mode isn't really the original image. And outside an expected drop in some PP quality, all detail is for the most part maintained. The issue is shimmering. If not for that, people wouldn't really be saying anything. I hope its something they can fix.
I don't know why they wet this route though, this looks like one of those situations where they should have just gone for a dynamic native 1080p -1440p or even better 1296p - 1368p.
While true I don't think that that overhead is close to 30%. Native 1300p would very likely look worse than 1800p CBR in the absence of TAAU - which is the main issue here.
I strongly doubt that native 1368p would look worse than what they are ding here. I mean even 1080p still looks good and is not a muddy mess with the right AA solution backing it. The issue is the visual noise whatever they are doing adding t the mage.