Take out Ovechkin's contract because it was signed a decade ago. Way too much has changed since then in regards to the salary cap and the CBA to use that as a serious comparable.
Add cap hit percentages to each of those contracts, and then you get a more honest look at where Karlsson is at. Toews and Kane's contracts would be the equivalent to about 12.2M under an 80M cap.
Subban's contract is the equivalent to about 10.4M under next season's 80M cap, and his resume at the time he signed the contract paled in comparison to Karlsson's current resume.
10.5M IMO is the floor for Karlsson. It's basically the Subban contract adjusted for the upcoming cap ceiling.
Unless Tavares or Doughty (or somebody else) pushes the ceiling higher before Karlsson signs, 12.5M is the ceiling. It doesn't mean Karlsson will get 12.5M, but he's in the conversation as a top player in the league not that far off from McDavid. Karlsson has been established as the league's #1 D to the point that the only time he isn't in the Norris conversation is if he has a season where he is hurt or has to play hurt.
GMs (and agents for that matter) know that barring some crazy unlikely outside situation (CAD hyper inflation, World War 3, etc) that the cap will continue to rise and in turn a player's overall percentage of the cap will deflate from season to season. Subban's contract is a perfect example of this. Right now, his contract is a steal because the cap his risen accordingly. At the time he signed it, it was a contract on the very high end. The contract still has 4 years left in it, and the cap has gone up enough in that time frame to make it a steal. Anybody signing Karlsson to a 7-8 year 12M type contract will know that 3 or 4 years in, comparable players might be getting 14 or 15 million.
I'm not sure I agree that it will keep going up. Attendance is down, and the cost of a night at a game is nearing a critical point in many markets. If the NHL wants to continue to fill the stands across the league I'm not sure they can continue the way they are.
I can understand a team running under the cap deciding that they don't want any players making 12 million a season. Hard to argue that there isn't merit to that plan. McDavid is the best player right now and even he can't carry what looks like a decent team out of the cellar. EK can't either, this isn't the NBA. People argue that EK carried the team last year, but while a romantic sentiment, it just isn't the case. We had several of our best players playing some of their best hockey. Take away playoff Ryan and playoff Andy for instance and we're likely out in the first round.
We need a balanced and deep team with an eye on winning the cup. To that end we need to keep control over salaries and not let outside market influences set our salary structure as much as possible. Between 10-11 is fair for a player of EKs caliber, who will have only one year in his 20's left when the deal starts, and the vast majority of the deal being paid out during the declining years of his career. As many like to point out, while he will still likely be an excellent player, statistically his best years are already behind him.
Arguing that he's the statistical anomaly who will only get better, may have a chance of being true, but shouldn't carry much weight during a contract negotiation that will see him paid until he's 37. McDavid was signed to 12.5 FOR PRIME MCDAVID, that is a 12.5 gamble you make, not a likely declining EK (still a great player, but not getting better).
Care and a cap is needed here.