Here's a couple 5on5 numbers:
McDavid xGF% with 0.55 without 0.44
Draisaitl xGF% with 0.52 without 0.46
Ekholm xGF% with 0.56 withou 0.44
Bouchard xGF% with 0.6 without 0.4
Makar xGF% with 0.56 without 0.54
Heiskanen xGF% with 0.52 without 0.55
Fox xGF% with 0.47 without 0.42
Montour xGF% with 0.55 without 0.53
Forsling xGF% with 0.52 without 0.55
Hughes xGF% with 0.6 without 0.45
In short, Bouchard with 0.20 has by far the strongest xGF% impact in 5on5 play out of everyone in the entire playoffs, at least of the ones who have played more than a couple of games and who play in significant roles, forward or defenseman.
The second-strongest impact is actually for Alexis Lafreniere with 0.16(0.52 with 0.36 without).