1, non-ProRAW output has always been ****** on all (less than about 8-9-year-old) iPhones - oversharpened mess. ALWAYS use ProRAW even if you only shoot 12Mpixels.
2, the 48 Mpixel mode, assuming constrasty subject and not extreme corners, indeed delivers VASTLY higher-res images even when just exported to HEIC or JPEG, even in batch mode, with MacOS' built-in, free Preview app.
3, low-light video performance is TONS better than previous iterations. I myself compared it to that of the iP11 (see my thread) and there's simply no contest.