I think in order to justify "the AI is a tool that a human is using, just like a paintbrush" you would have to have to define what meaningful creative process that the human has followed while using the tool.
In my opinion things like selecting a training dataset and then writing prompts are not creative processes they are mechanical processes. Input in, output out, with barely any interaction from the human.
Consider when you commission an artist to make a painting. You give them a "prompt" by explaining what you want. Maybe you even give a "training dataset", a few examples similar to the look and feel of the result you want.
Then they go off and make something. They show you in process stuff and you make suggestions so the next version they show you is closer to what you want. This repeats until you are both happy. Then you own the drawing. Because you paid them for it.
In this case however it's absolutely clear that you did not create the work. You had input into the creation, but the artist was not a tool you are using to realize your own creative vision. They are the creator, you're a customer for them.