It's astonishingly simple to train both LoRAs and Embeddings nowadays -- if you combine it with tech like ControlNet, you can more or less have direct control over the illustration as well (see this example I converted to Hollie Megert's style with barely any effort [1] using the model from [0]) -- but FWIW I was playing with the WhatsApp AI stickers recently and human-made illustrations still have a "je ne sais quoi" that sets them apart, vaguely reminiscent of "realistic" animation vs. "squash and stretch". I would not be worried as an artist*, but I would be worried if I am making assets for corporations in Corporate Memphis [2].
[0] https://waxy.org/2022/11/invasive-diffusion-how-one-unwillin...
[1] https://i.imgur.com/ZwtKug5.jpeg
[2] https://en.wikipedia.org/wiki/Corporate_Memphis
* In fact, I think I'd be excited, it can be a great tool, and people who lack artistic sensibility might find it almost as hard to use as to make art themselves. However, I do think there needs to be some kind of protection from having your 'style' commoditized without consent, using unauthorized images of your own art.