I think their definition of fair could be different than ours. The ownership are not afraid to pay on one hand, but they are pretty hawkish (and always have been) on player compensation. The leverage of the trade is a little silly - since nobody is going to offer a reasonable return without some sort of confidence Lester would resign. So yes, if there is leverage in the "well if he doesn't sign we can trade him to Milwaukee for a bag of donuts" - that is leverage. But from a practical scenario the player has much more say.
That said, if the Red Sox re-sign Lester, it will effectively be a "last contract" - since Lester's 10/5 rights will kick in.