The UX totally kills Gimp, like it hinders LibreOffice, especially in comparison to Excel. Let's not forget many pupils have little affinity with corporate IT and no interest in learning text editing for the heck of it. If you have to teach it anyway, best give them easy tools that they can recognize later in life, and with which they can help their grandparents.

Given the fact that IT teachers are scarce (at least here; teachers for programming aren't available at all below advanced educational levels), I do think that simply foregoing teaching these skills might even be better.