I'm not an artist nor a photographer, but it is apparent that LR is heavily biased towards going back to a RAW file and converting it to an image using their ACR de jour. PS can use the ACR as a source, but layers can also be composed from numerous other sources such as the outputs from dozens of RAW converters, image processors, stackers, stitchers, scanners, etc. That makes it far more versatile for my needs. I'm sure that for photographers and other pros it is more efficient and productive to use the jack-of-all-trades Abode.
EBH