Well, in all honesty, you could put Patrice Bergeron in between those guys and they'd still probably bleed shot attempts. One guy, even at center, isn't going to move the needle that much unless his wingers also elevate their defensive game. I also hope we'll see some adjustments in the overall defensive structure that will lead to better defensive metrics overall. Perhaps they start with something simple like not giving up the blue line like it's a yellow Starburst.
The other thing is that we all as fans love to project lines before the season starts and we're almost always wrong. So while we assume we'd bring in a guy to skate with Panarin, it could very well not work out like that. That's why I would be looking for someone with positional versatility, that also might not look out of place centering a 3rd line or even skating as a winger. Bringing in someone like Monahan is a huge swing and really great on paper but if he and Panarin are like oil and water suddenly things are way out of whack.