'Collective reality' doesn't apply when you're talking about the top 5 dmen in the league. Predicting the career trajectory of a top 5 dman (and one-time undisputed #1 dman) based on the top 210 dmen in a given season is useless. That would be most of the dmen in the league, wouldn't it? 31 teams x 7 dmen equals 217 players. I don't think data on the #7 dman of the worst team in the league is particularly relevant to Karlsson.
Karlsson is clearly playing injured right now (groin or hamstring by the looks of things) and his skating is severely affected, and yet up until yesterday was leading all dmen in playoff scoring (1 point back of his partner Burns now). Players of that skill level adapt when circumstances change. It's why Lidstrom was able to remain effective despite losing a step in his 'old age', and why Datsyuk was still able to make Abdelkader a 20-goal scorer with 0 tendons in his ankle. An average player gets hit with an injury that slows him down, or loses some skating due to age, then it really affects them because the margins are that tight when you're an average player. Players at Karlsson's level have a lot more wiggle room to adapt because of the large skill gap between them and others.
The only thing to worry about with signing Karlsson is a career-ending injury, but that's a risk with any player.
I'm not saying he won't, I'm just saying that the risk is greater than it once was.
For examples against, I'd ask what happened to Drew Doughty (someone you mentioned the Leafs should shop Matthews for)? Was he worth his $11 million hit last year at 29 years old? How might it look at 33, 34, or 35? What about Shea Weber and PK Subban in 18-19? How about Kevin Shattenkirk, Suter, or Yandle? Were any of them top 5 this year? Did they sniff top 10? Minus Suter and Yandle, one could make an arguement that most of those guys were top 5 D men at some point, all were top 10 IMO.
Love it or hate it, here's the CF% for this year:
EK is pretty much tops, so it supports your opinion, I just don't like the odds of sustainment coupled with the Wings current roster strength. That said, I've been wrong plenty in the past. If he's signed, I desperately hope I'm wrong. Maybe if the roster were minus Abdelkader and Neilsen, I'd be more fond of the idea.
How much should the toxic cap space (Abby, Neilsen, Weiss, Ouellte, LTIR) overage) influence this sort of decision?
Whatever happens, in Yzerman I trust.