I think the "cruel and unusual" clause requires both to provide any protection.

It's self-evident that most of the actions of the criminal justice system are cruel. I think anyone would agree. However, that phrase in our constitution explicitly leaves the door open for our criminal justice system to perform cruel behaviors, as long as they are in line with the standards of the day (or, if you're an originalist, of the standards of 1791).

So, my response would be that you've tabled the only portion of the debate that is relevant. I'll freely concede that the criminal justice system is cruel, but I wouldn't then argue that the system falls afoul of the 8th amendment.