Earlier quoted context omitted.
Again, I don't understand your point. GVim is GUI, not TUI.
A GUI can draw vector graphics, like lines, arcs, arrows etc. GVim still behaves like a terminal, which just has a grid of characters to work with. Any such vector graphics is done awkwardly with fonts, which doesn't give the best result, and patching fonts is not the best UX.
And I don't see how such features are necessary to rule GVim as GUI. I have a fairly basic classification: TUI runs in a terminal, GUI have their own windows.