Not sure I agree with this. I wrote a bunch of data vis GUIs with PyQt and Pyqtgraph, all Python, with everything keyboard shortcuts and accelerators, and it was Vim-like speed except where CPU bound by data processing (NumPy).
So I think it can be fairly easy yet Qt dies (frequently, on HN) on the altar of native look/feel/platform (ie doesn’t look/feel like a MacOS app on macOS).