Wii is blurry on the horizontal axis however you do. This is because the internal frame buffer is maximally 640px wide, which is then stretched (interpolated, thus “blurred”) to the output 720×480 frame, where it normally takes up 686 of the full 720px width (at least in widescreen, I didn’t measure in 4:3 mode, but it should be the same). Additionally, the maximal height of the internal frame buffer is reportedly 528px, meaning that some games may even interpolate on the vertical (although I don’t know how common that is or if it was even a thing).
EDIT: actually I checked the excellent list of Gamecube games internal/external resolutions here, and it seems vertical interpolation was very rare (actually non-existant for NTSC titles and only occasionally for PAL game). I would assume the situation is the same for Wii games.
For reference, the actual height of visible video was 456 lines for all games I’ve tested (as well as the dashboard) except for Metroid Prime 3 (448 lines high).
To summarize, the search for immaculate “sharp pixel” Wii output is a dead end, and actually counterproductive as the horizontal smoothing process was very intentional to improve the appearance of these still pre-HD games.