
There were action, romance, comedy and lighting specialists just to name a few. These people didn't do the whole film, just the parts that lent itself to what they do well. Today advertising still follows this practice. A beer commercial will call in a glass photography specialist to film the close-up where the beer pours into the mug. That seems perfectly natural to me.
The question I'd like to pose here is, why doesn't the animation industry follow this practice?

The audience doesn't want to see the best that a particular unit can produce, it wants to see the best that possibly can be created, no matter who does it. My advice to both TV and feature producers is to build time into the schedule to run some of the finished scripts and storyboards past appropriate specialists for a punch-up.