Instead of changing the PP groups, why not try different tactics first?
It's pretty clear that opposing teams are collapsing down low whenever the puck gets to Reilly, mainly because they know he's not shooting. They tighten up more when he passes off to Marner or Matthews. This seems like a pretty easy thing to counter.
First: Have Reilly walk in and draw a defender out to him. If they do, it opens a lane; If they don't, two Leafs move to the front of the net, he shoots.
Second: When Marner gets the puck on the right wall instead of looking for the seam (which he never gets now), move farther down, as far as the goal line while Reilly moves in. Spreads out the defenders and has them looking in more directions.
Third: Marner again with the puck on the wall. Matthews moves to the high slot, Tavares dips to the far post. This forces one of the defenders to choose. The other player is open.
Fourth ... I mean, anyone coached at any level here? With that much talent, even without a legit howitzer from the point, there's so many options. Babcock has tried about one of them (switching Marner and Matthews). Doesn't make any sense.