Leafs don't need to panic, they simply should have addressed this in the off season. You can win a great number of games but if you leave yourself open to any deficiencies other teams will exploit it. Even inferior talent can win games if they get the lucky bounce or PP to win a game 5-4
Ultimately, I think Babcock is convinced this defense can elevate and succeed based on some of his comments. It might even be him behind the scenes suggesting it to Dubas and others, I don't know, I only speculate. However, I suggest that this is where the GM, President and others have to say "the facts don't lie".
If you want to know what is a concern to your team, find someone to ask honestly (if you can get an answer) from other teams coaches what they tell their team to do against the Leafs. It will be the same right? Try and clog up the middle, don't take penalties and drive hard through their defense.
I recall the Habs of a few years ago that had stellar defense, a great number of shot blockers and the best goalie in the world in Price on top of his game. They made it to the final four once, never addressing their achilles heel, they couldn't score goals, they always believed that the group they had could get it done, they didn't. I saw the potential of a Cup team there, but they never got over the hump.
Leafs need to learn from history and others mistakes. Improve the D, the better deal they can make for a stud the better their chances. Even if it's at the expense of some depth up front.