I am not missing the point. Would I like a bigger, meander defenseman in that position? Sure. Is one available? No. Could one become available in the next two years? Maybe, more likely not, or maybe the price will be way too high (see Chychrun). So you just bleed out for the rest of this season and two more in the hopes that an opportunity does come along? What if it never does? Even if they have McCabe, and another opportunity comes along for a defeseman who is a perfect fit, good teams make it work. You flip McCabe or someone else, you do what you need to do. Maybe you trade Roy and get a partner for McCabe who has size and snarl. Look at TB or Colorado; they do what they need to do and manage the cap with a lot of expensive contracts.
Also, you're also seriously undervaluing Roy and likely Walker. Roy gets a decent return, you don't have to add to trade him. Right shot D are valuable, and he's a legit second-pairing RD on a lot of NHL teams. I bet you could get something in return for Walker, too.