> What you described is entirely fair use, actually
Just like during the pandemic how everyone became an epidemiologist, suddenly everyone's a copyright lawyer. I'll just dispute your assertion by saying:
1. Questions of fair use are famously gray, and anyone who declares something as "entirely fair use", with no caveats, is nearly always wrong except for the must obvious cases, which the given example is most definitely not. A judge has wide latitude in determining fair use.
2. People should familiarize themselves with the four factors of fair use determination. In particular, if a work is purely derivative of a source work and substantially negatively impacts the market for the original work, it's very likely to not be considered fair use.
A great overview is https://fairuse.stanford.edu/overview/fair-use/four-factors/