Toews and Kane took what they thought was fair based off where the salary cap was going. Unfortunately they didn't forecast the economy properly, so the cap didn't jump as much as it should have based off their projections.
Now the cap is jumping to where it should be, but because of those contracts being extra inflated due to the cap not rising, and the Seabrook Bickell deals, they had to let go of damn good players and couldn't get much back as they were stuck in a bad position.
Tough to blame the Toews and Kane deals, but lots of blame can be given on Seabs and Bicks, along with a few trades since the last Cup.