for most of his time with us mcphail played very deep, but his role was crucial to us in spreading the play and setting up attacks.
there are some interesting ways people have tried to address this conundrum, one of them is to look at xG of shots, then attribute that xG to everyone who had a possession in the side building upto the shot. then also subtract any xG from all the players who were involved in possessions that led to the opposition having a shot.
with time you'll build up a picture of which players are helping the side generate the most xG.

that's a fairly basic one, there are other ones like bypassed defenders etc that would give a better picture than goals and assists.