A quality artists that's flexible enough to take on whatever the clients needs are, has a fundamentally deep understanding of the world, human beings, physics, anatomy, phycology, story telling (thus having a full deep understanding of reality), etc.

For an Ai to replicate that it would have to be an AGI.

Working with Ai artists is gambling. You're hoping that whatever you asked of it, it will be able to do well and to your specification. They can NOT do most tasks well.

If we were to compare Ai artists, to self driving cars, they are less capable than self driving cars were 40 years ago. Self driving cars 40 years ago could drive on roads and stay in the lane, which is most of driving. Ai artists can draw humans in a very limited set of poses from a very limited set of angles. They fail with anything that they haven't had a massive amount of data examples to learn from.

Self driving cars have also been 5 - 10 years away from fully autonomous for over 40 years, as presented by the media and researchers in the field. It will be the same with any "Ai hard" problem. They won't be fully solved until we have AGI, which means the best humans in those fields will still be able to find work.

As far as your janitor, robots are coming for that job. Maybe not next year, but Google, Tesla and other labs are making significant progress towards a Robot that could automate that job. These robots can visually identify objects, pick them up and use them, and do complex reasoning and problem solving about their environments. It's the same though, it won't be able to solve every problem a human janitor could, so the best janitors will be able to keep their job until AGI, but there will be less janitors over all.

We already have robots that vacuum, clean, and mow lawns. So robots are already eating into that field.