I am pleasantly surprised by the Minolta MD 45mm f/2 that I got at KEH for $65, so I decided to compare it to the RF 45mm f/1.2 that cost me $470. First, the Minolta is tiny.
Second, although the Minolta is old school tech from 1978, it actually competes pretty well in sharpness at apertures above f/4. The corners are never as sharp as the Canon, but the center is pretty damn close at almost every aperture. I'm not going to spam the forum, so here's a sample at f/5.6. Canon on top...