Don't think you can really do math that way. The thing with contracts is unless you're top of the line the longer you wait the less you tend to get. My take on this is Toronto wanted to do a quick deal to be done with pitching in FA and focus else where. So, they probably over paid on a guy they had before and like. The thing is, if Lackey hasn't signed by January most of the teams after him will be gone and he will have to settle for what he can get. For example, most thought Shields would get more last offseason but by the time he had signed a lot of teams had spent any remaining money they had in their budget.
In the case of Lackey and Shark, both have QO's tied to them and if I'm not mistaken, Happ wasn't offered one. So, in that regard, you can also look at his contract as non-draft pick tax. Additionally, Happ had a big uptick in performance under Searage who many think is a god among pitching coaches similar to how most cubs fans view Bosio. So, there's reason to believe in him $12 mil isn't really that much if you're wrong. I mean look at where the cubs are with Hammel. He's making I believe $9 mil.
With that being said, I figured Lackey would get $15 mil regardless unless no one went after him because if he thought he'd get less you would just take the QO.