I feel like before this thread gets too "the old masters (and maybe current ones as well) are just overrated hacks" it's worth mentioning that most of the techniques that from a distance may look like cheating do actually take skill to apply properly. Any digital artist probably knows what I mean - some non-artists are dismissive of digital art because they think "the computer does everything" while those of us who actually work in the field know that's extremely far from true.
If we are to talk about "assembly line work" in art there's probably no better example than American superhero comics, which have broken down the process of making a comic into many specialised roles: writing, pencils, inking and colouring are all normally done by different people in a rather short amount of time, using characters and an universe that someone else designed a long time ago. But even if it can be called "assembly line work" due to the process, this still takes a lot of skill to accomplish (even if said comics are not to everyone's taste).
And it's also worth mentioning that there are artists who don't trace (probably a majority), and there always were. The process of making art is very personal, and dependent on the specific person's strengths and weaknesses, as well as their living situation. For instance, commercial demands may drive an artist to use shortcuts they normally would not resort to, just because they need to work a bit faster and feed their family (or heck, themselves). And the requirement to work both very fast and to very exacting standards has only increased since we have started creating long form animation, video games and similar projects that (usually) have large art teams working together towards the same goal. It's never been a terribly well paid profession, except maybe for those at the very top, and even that is not always a given.
