Like I said before, Edmonton is a good team, and is expected to be good for the next few years at least. I think we can all agree on that. I also think that on paper their playoff roster last year was better than Florida's.
In fact, after a quick google search from what I can tell (I am not a gambler), all of the major betting sites have the Oilers as most likely team to win the Stanley Cup next year (either +800 or +850) depending on site. In this list, I am including each of DraftKings, FanDuel, BetMGM, Caesars, bet365. Every single one of those sites has the Oilers as most likely team to win next year (around 10% chance implied odds), no team has better odds on any of those sites.
sportsbook.fanduel.com
Compare this to the 88 Kings -- when Gretzky joined the Kings they had been sub 0.500 for the three previous seasons and hadn't won a playoff series in 6 years. The situations aren't even remotely similar. That's not even close to where the Oilers are now, in what should still be close to McDavid's prime based on his age.
***
Anyway, unless McDavid gets traded to or eventually signs with a team that was not contending prior to his arrival, your example of Wayne Gretzky's Kings is completely irrelevant to this particular discussion.