Notice the “and” and that it’s not an “or”?
“cruel and unusual” has entirely different implications that “cruel or unusual” which is essentially how too people seek to apply the standard these days.
A punishment can be very cruel but if it is a not-unusual possible punishment for a given crime it is NOT cruel and unusual. Likewise a punishment can be downright odd for the given crime but if it’s not cruel then that too is okay.
Interesting argument. Is that the generally accepted position of constitutional scholars?