Also, don't underestimate the value of a guy who can be a quality partner.
Not mentioning any names but I seem to remember another excellent Rangers defenseman who got taken to the sixth circle of Hell by his partner.
I think this is why ranking players or labelling them a number can be a bit fruitless at times, especially for defensemen. A defenseman could be great on one pairing and not on another depending on how they fit with your partner. Guys who can play well with anyone as well as complement a high end defenseman are hugely valuable, even if their ceiling might not be as high as some others. Canucks saw that for years with Tanev