>PC CRTs would always be quite sharp, due to VGA, no matter whether it (the CRT) had a low or high resolution.

VGA CRTs are always "high resolution" compared to the SD CRTs discussed in the article. If you display a mode 13h DOS game on SD CRT, which is possible with special hardware, it will not look as sharp as it would on the VGA CRT is was designed for.

This sharpness from using higher resolution CRTs is in addition to the sharpness from using RGB connections. And if you somehow manage to connect a VGA CRT over composite, it will be less sharp but still sharper than a SD CRT over composite.

The point is there are two factors here: the sharpness of the CRT itself and the sharpness of the connection method. The article only talks about SD CRTs, so the CRT's sharpness isn't going to make much difference there. But when you consider MS-DOS games, which used sharper CRTs, the CRT's sharpness becomes important.