I recently-ish wrote a GPU based renderer for a GUI toolkit. I haven't put a ton of effort into optimisation, so I wouldn't be surprised if for smaller windows with lots of elements the GPU renderer was slower, but once you get to high-dpi displays with larger windows the CPU approach hits its limits. I don't have hard numbers, but we went from an unusable ~15fps at 8k resolution to hitting our target of 60fps with the GPU renderer.
If you use froward rendering, which means placing a bunch of textures on the screen, you are not really "drawing". We are probably not talking about the same thing.
It's not as complex has say drawing SVGs, but I've implemented Bezier curves, stippled lines, arbitrary rounded rectangles (html style) and subpixel-antialiased font blitting. I'd say that's far from just "placing" a bunch of textures.
