I always thought the Steve Smith own goal was too bad. Calgary was very good and maybe they still win without it but I feel like Gretzkys career is essentially perfect with 5 straight cup wins. In my mind the 86 playoffs are the only blemish.
You know what? Even as a lifelong Oilers fan, I don't really mind the 1986 loss.
Calgary was clearly the better team that series (in four games at Northlands in Edmonton, the Oilers won a grand total of ZERO games in three periods). Hard luck to the Oil on the series winning goal, but they had not played well enough all series.
The Oilers' Dynasty had two major "shifts" -- one was after the 1983 sweep by the Islanders. Gretzky assumed the captaincy, but it was a case of the young guys suddenly having to become team leaders. They decided to divide the next season into games vs. Campbell Conference opponents and games vs. Wales Conference opponents, to make sure they were ready for the Eastern teams in case they met in the Finals again. Then, the second shift occurred in the summer and autumn of 1986. After the Calgary loss, the 1985-Oilers' hockey (high octane with 'miracle' saves; Coffey going end-to-end; and, because of rule changes, 4-on-4 dominance) ended. It was all business after that, with the regular season becoming merely a necessary burden. In the '87, '88, and '90 playoffs, the Oilers were able to play two-way hockey very well, including locking it down defensively quite often.
All of which is to say, I'm not sure the Oilers even in the '87 and '88 Cups if they hadn't lost to Calgary in 1986.
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The fly in Gretzky's legacy-ointment, as I see it, is the Kings' loss in the 1993 Cup Finals to Montreal (or, if you prefer, the Kings loss to Edmonton in April 1991 -- the best team Gretzky played on after leaving Edmonton).
I strongly believe that L.A. -- despite being, in some ways, a very weak Cup Finalist (as the following season showed) -- would have won the 1993 Stanley Cup if not for Marty McSorley's stick.
Being able to drag L.A. to a Stanley Cup, well into the '90s, would have been the ultimate capper to Gretzky's legend.