(accidentally deleted my post in editing it!)
The gist of this post was to say, let's not overrate Coffey's effect on teams' offense. Gretzky scored 164 points at age 19/20 on a team with Coffey scoring 32 points. And, as noted, his PPG in 1988 was slightly higher than in 1987 with Coffey.
The Oilers scored 372 goals with Coffey (and Gretzky playing 80 games) in 1987, and then scored 363 goals without Coffey (and Gretzky missing 16 games) in 1988. Negligible difference. And the Oilers scored more goals per game in the '88 playoffs without Coffey than in the '87 playoffs with him.
(I mistakenly said, when I first posted here, that Coffey played every game in the '87 playoffs. He actually played only 17 of the 21 games. However, in one of the games he didn't appear in, the Oilers scored 13 goals.)