Wikipedia lists SN1054 as mag -6. The distance differential gives an extra 5.3 magnitudes. That means before correcting for differing levels of dust/gas in the path (call a PHD) it only goes up to -11.3. That's about 4x dimmer than the -12.92 magnitude full moon, and 2 million times dimmer than the sun.
IIRC Type II SNs are fairly variable in luminosity, but while that might get us to brighter than the full moon it won't be anywhere near the suns luminosity.
The post on doomers.us appears to be engaging in massive brightness inflation
IIRC Type II SNs are fairly variable in luminosity, but while that might get us to brighter than the full moon it won't be anywhere near the suns luminosity.