Qt and GTK I could see being seen as 'cartoonish' because the default themes on many distributions are fat, shiny, bubbly, and look like they firmly belong in the 2000s.
Cocoa, maybe because of the vivid blue? Or that person hasn't seen Cocoa since before they moved away from the glowing blue bubbles, although I think they still look nicer than Material.
Qt and GTK I could see being seen as 'cartoonish' because the default themes on many distributions are fat, shiny, bubbly, and look like they firmly belong in the 2000s.
Cocoa, maybe because of the vivid blue? Or that person hasn't seen Cocoa since before they moved away from the glowing blue bubbles, although I think they still look nicer than Material.