If you watched Las Vegas, Gallant even had guys like Marchessault back checking.
And Ghost playing defense hasn't hurt his offensive game, nor has he been asked to play like Provorov, rather, just some basics, like getting back on defense, using the body to get between a forward and the goal instead of just stick checking, and on offense, dumping the puck in when pressured at the blue line instead of turning it over.
In the same way, all they want from TK is to use "hockey sense," and play 200 feet. Don't just hang at your own blueline cherry picking, hoping for a pass when your defensemen are being pressured. And don't make dangerous cross ice passes that can result in breakaways unless you're sure it won't be intercepted. He's already an aggressive forechecker and willing to hit people, he just has to know when to be aggressive and when to get back.
You're not going to take a guy who lacks great instincts and have him play like Couts or Patrick, which is one reason Hextall is drafting a lot of guys with those instincts (Frost, Farabee, O'Brien, Rubtsov, etc). Some guys are just limited, I think Laughton just doesn't get how to play in his D-zone. But most players can improve on defense to the point where they're not a liability, even if they'll never be mentioned in the same breath with the Selke. Most of playing defense is the desire to do so, the key to back checking is primary the willingness to skate as hard going back to your goal as you did trying to score. When the defense can't get the puck out, it's often because the forwards have headed up ice instead of helping their teammates.