The existing evidence includes the typical experience of people new to FOSS using things like Emacs, VIM, Gnome or GIMP...
Bad usability and a high learning curve are not the same thing. A high learning curve is what makes people "new to FOSS" have difficulty with emacs/vim, not a lack of usability.
And Gnome is also a bad example, since it is both usable and has a minimal learning curve. At my last job we set up a crowd of 30 fashionistas (no tech background whatsoever) using gnome with no real issues. Several of them also used inkscape with little difficulty.
Try to change font faces or default frame parameters on Emacs. You could describe that catastrophe as a high learning curve, but I think it's a usability problem. This is just one example.
Bad usability and a high learning curve are not the same thing. A high learning curve is what makes people "new to FOSS" have difficulty with emacs/vim, not a lack of usability.
And Gnome is also a bad example, since it is both usable and has a minimal learning curve. At my last job we set up a crowd of 30 fashionistas (no tech background whatsoever) using gnome with no real issues. Several of them also used inkscape with little difficulty.