5 million is pretty standard for a 1st line blueliner. Signing Subban long term at 5 mil per is probably going to be a steal for us in the long run.
There's risk in ANY contract. Look at OV, could you have forseen him crashing and burning? Of course not.
If the discussion was paying PK 7 years at 7 mil per I could understand what you're saying but he's already a 5 million dollar player today. We have to assume he's going to get better dude he's only 23. So you sign him and hope that he gets better. If he stays the same, it's still not a bad contract.
5 millions is still good money for a less than 25 years old RFA defenseman on a long term deal, even when they are first line.
Erik Karlsson : 6,5 millions cap hit for 7 years
Erik Johnson : 3,75 for 4 years
Alexander Edler : 5 for 6 years
Keith Yandle : 5,25 for 5 years
Kris Letang : 3,5 for 4 years
Michael Del Zotto : 2,55 for 2 years
Jack Johnson : 4,357,143 for 7 years
Drew Doughty : 7 for 8 years
John Carlson : 3,966,667 for 6 years
Alex Goligoski : 4,6 for 4 years
Zach Bogosian : 2,5 for 2 years
Cam Fowler : 4 for 5 years
Dmitry Kulikov : 2,5 for 2 years
Doughty and Karlsson are better no question, the others are all debatable (but IMO Yandle is better).
Looking at this list, 5 millions for 5-6-7 years is a fair deal for PK (it would put him in the better paid of the list if you exclude to two players that are surely better than him), but it's clearly not the steal some are making it out to be. It's not the kind of deal that increase a player value in a trade compared to a 2 years deal at a smaller cap hit. Like you say very well there is a risk with long terms deal, looking at Ovechkin right now.
Also looking at young studs like Kulikov, Bogosian and Del Zotto with 2 years deal at 2,5 millions, I fail to see the how much ''insulting'' this offers are like some are trying to say, especially since in the Subban case I see Bergevin starting with that to negotiate and have Subban accept something like a 2 years 3,5-3,75 offer.