Image processing is probably offloaded to some sort of custom silicon. If that is the case, then the generational performance uplift would be massive.
Consider this:
Decoding a big fat X265 file on your 2012 MBP would be atrocious because it doesn't have hardware X265 decode, but decoding it on your XS would probably be fine.
That could be true for only some algorithms but I have investigated the source code as well and on ARM it uses only NEON instructions if available (but its equivalent of SSE and AVX2 on x86 anyway).
The result is the same with my own crafted image processing algorithms using single core. Apple makes really fast CPUs.
Consider this:
Decoding a big fat X265 file on your 2012 MBP would be atrocious because it doesn't have hardware X265 decode, but decoding it on your XS would probably be fine.