The amount of stuff you're making up here is staggering. Let me attack this point-by-point:
The Sox overpaid Porcello in money to underpay in years. This is not rocket science and it's not something that's even worth arguing about. It's the Sox' strategy to avoid paying pitchers past their prime. No matter how much you (or anyone else) wants to whine about it, it's a wise business strategy for a team with this kind of money. You pay a premium to avoid clogging up a roster spot long term with an aging player, because in the grand scheme of things, it doesn't hurt you as much as it would hurt, say, the Rays. It's simple.
Lester is not an ace, and he's exiting his prime. He's exactly the kind of pitcher you don't pay 25 mill a year for six years. Recent late-contract implosions from star pitchers Roy Halladay and Cliff Lee are very good barometers for what Lester's last 2-3 years may look like. He's high-risk, and overpaid in terms of both years and money.
That's not his market value, that's the market value of a pitcher who's both better and younger than Lester.