Obviously no one was going to match Gretzky's ability and production, but I almost think we forget the talent that was acquired for him or selected with the assets in that trade.
Martin Gelinas was an 18 year old scoring sensation drafted 7th overall by the Kings a few weeks prior. He was a member of the Kid Line, which was instrumental in the 1990 cup victory. He scored 300 goals and played 1200 games in the NHL.
The Oilers also received three first round picks which ended up being the 18th pick in 1989, the 20th pick in 1991, and the 16th pick in 1993. One of the players became Martin Rucinsky, who played 900+ games and scored 241 goals. So when all is said and done, the Oilers ended up with two wingers who scored 550 goals and played 2,100 NHL games.
From an asset management standpoint, those other picks easily could've been names like Jason Allison, or Saku Koivu, Todd Bertuzzi, or Adam Foote.
So, in hindsight, the biggest thing that probably held the Oilers back was how they used the picks and asset management.