The main problem is that both Rielly and Marner are sub-par shooters.
The game plan is simple:
1. Take away Matthews shot.
2. When Rielly/Marner have the puck, let them shoot but take away their passing lanes.
The other issue is that the Leafs don't try to create downlow plays/backdoor passes. So the PK just has to be aggressive against the points (Rielly/Matthews/Marner) because the Leafs aren't even thinking about trying to create high-t0-low plays.
I think this is more the issue. Matthews is up way too high so when he gets the puck, he needs to skate into a better spot before getting a shot and the lane is gone by then. Same with Marner. He is up too high and the defense closes in before he gets to where he needs to be to make a play besides passing it to Rielly. Rielly is resorting to passing to these guys who are not in dangerous positions or forcing something that almost never works.
The solution is that Marner and Matthews have to set themselves up better off the puck and let Rielly get them in places where the quick plays (Matthews shot, Marner pass) can happen and lead to goals. We have had a few opportunities like that (even on the 4 minute PP we had a couple), but for some reason they have mostly strayed away from that since Matthews' injury... Even though Matthews is healthy again.
Rielly should be given more ice up top to wheel and have guys in positions down low for him to get it to them. Marner should be closer to the hashmarks rather than at the blueline like he is another defenseman. Same with Matthews. Unless Rielly has chosen to wheel down low or is really committing to one side and there is no lane to the opposite side anymore, those guys should not be at the blueline. Ever.
Rielly doesn't have a Weber shot but if he is in space and can skate into his wrister, or even gets a one-timer between the dots and anywhere below the top of the circle, that shot needs to be respected. Even if it doesn't go directly in, it leads to great rebounds, easy tap-ins, and easy deflections. Another thing they have stopped doing unless Marner is setting Rielly up because they have no better choice. Rielly should never be the first choice when you have Matthews, but he is still dangerous if he gets the puck in space.
It's really not a huge adjustment, but it has been the difference between our 40% PP and our 4% PP.