I don't get this "defensive shell" complaint. Every team does it. I don't want these idiots making risky plays in their own zone. "Let me just swing this pass through the middle of the ice..." Hell no. You've got no options, chip it out. Don't force passes. And don't get caught on the wrong side of the puck, either. Man, you'd get crucified if your guy scores while you were cheating for offense. But that's all it takes for the ice to get titled sometimes.
Hockey is an aggressive sport and if you don't keep pressing the other team, you are doomed. The defensive shell strategy has been shown time and again to be more detrimental defensively than being aggressive. Sometimes a good team manages to weather the storm, and that survivorship bias combines with a fearful coach's aversion to liability to justify what is objectively an awful choice and awful system. It looks worse when you lose a one goal lead because you gave up an odd man rush against than when you give up the lead because you committed to managing risk but a shot from the point managed to get deflected in. The first, the coach feels like was their and the team's fault while the latter feels like unavoidable bad luck. That's the only reason this system is used. It's just fear.
If the other team knows that you're not trying to score, they have total impunity with the puck. They can make risky plays and count on the fact that they'll just get it back if the risk fails. Their D can press forward without fear. Their forwards can play loose and free. Defending is demoralizing and exhausting. Playing offense is fun and invigorating. You give away all of the momentum when you play to manage risk. I'd genuinely rather that we play every minute of every game like we're down a goal than ever play this way. I'd rather that we continue to generate offense, and put fear in our opponents instead of becoming afraid ourselves. If we have the puck in the defensive end and we're choosing between systems that result in these outcomes:
System 1: 2 dangerous opportunities for, 3 benign opportunities for, 3 benign opportunities against, 2 dangerous opportunities against
System 2: 2 benign offensive opportunities for, 8 benign opportunities against
I will take system 1 every single time, even if we're winning by one goal with the clock running down. Even when the other team scores on you, if you're running system 1, your team can recover. If you're running system 2, it's so hard to switch back to an aggressive mentality. It's so hard to get the other team off their game again. Once you start playing system 2, you've accepted losing the rest of the game. You just hope to lose sufficiently slowly that you're still ahead at the end. Choosing system 2 screams to everyone "we don't think we deserve the lead we have. We believe that we're the worse team and we're desperate to turn our lucky lead into a win. We believe that if we lose this lead, that we cannot recover." We choose system 2 every time, and we lose because of it.
Safe is death.