What's the responsibility of the low man on the PP, then? Just give it back to Backstrom every time?
Once set up, the player is the outlet for high pressure situations on Backstrom. Additionally, they have options for a quick pass to the slot (or in rare situations, the point). When nothing presents itself, then they return pass to Backstrom or rim around to Ovechkin.
When the puck is on the weak side, they either rotate to provide an outlet for Ovechkin or sneak into the slot/crease.
The biggest role is zone entry.
If the man in the low position has the puck then Backstrom and the slot player typically form a triangle with Ovechkin as the X-factor option. The PK can't commit 3 players to handle all 3 PPers in that triangle unless they want to really collapse and leave either the point or Ovechkin uncovered, or a man shading both. So someone is often open, usually Backstrom who is in the worst position to shoot, but sometimes someone else.
The man in that low spot ABSOLUTELY is looking for Ovechkin. I would say that's the 1A option for just about every other player on PP1. For that low position, the slot player is probably option 1B or 2 with Backstrom as the release valve. Getting the puck to Ovechkin vs a diamond can be a matter of getting past 1 or 2Pkers, same as any other pass, not 2 or 3, depending on what just happened before to get PKers in or out of position.
To get the puck to Ovechkin, they have to get the puck past the LD and the goalie at the absolute minimum, and likely the RD and the forward shadowing Ovechkin as well. Sure, they can look for that option, but it's not going to be there unless the defense has completely broken down. Getting the puck from the goal line on the right side of the goal to the left circles is passing through the most valuable scoring areas, which in turn means the most hotly contested areas on the ice during a PK.
If Mojo is not a threat to take the puck to the net from that low spot then teams will not bother covering him. They'll just cover his passing options, including the point and Ovechkin, and then the PP can't do anything. This is exactly what happened at some point and it became necessary to try someone else down low (Ward? Kuz? Bura? I can't remember who was used but that person immediately started pressuring the net from that position and the PKers had to change their approach).
Look at the heat map I posted previously. Johansson is absolutely a threat from down low. Neither Ward nor Kuznetsov were ever used in that spot on PP1, and Burakovsky was only there very briefly during the regular season. The other options for that down low spot were Laich, Chimera, and Glencross, and they were predominantly used on PP2. It's a left-shooting location.
I think dynamism absolutely is required of that low spot if it's going to be played effectively. A player behind the net is a potential threat to the defense, especially in a man advantage situation. He can force the entire defense low and out of position. He can draw a single man and outmaneuver him, creating even more of a numbers advantage for a second or two, and possibly a shot. He can distribute the puck to the other 4 players in a great position for them to shoot, as he can see the entire play from the perspective of the net and feed a pass directly to a player's stick from in front of him. He can drive the net from either side, or reverse the puck.
None of that requires dynamism. All of that requires accurate passing and driving the net, which Johansson fully executes.
And once again, the premise that Burakovsky is far more dynamic than Johansson is flawed to begin with.
I'm not sure its a fair comparison because when Mojo's been taken off its been for guys like Chimera, Beagle, and Aucion. We've never given someone with more skill then Mojo a shot (IE: Kuzya or Bura). I'm pretty sure Kuzya could fill that role easily, or Backie can and Kuzya could swap into his role.
Grabovski filled that role while he was here and healthy. It had immediate impacts, but ultimately was more or less on par with Johansson. Putting Kuznetsov or Backstrom into that spot would be a waste of their talents.