I see your point but your comparison doesn’t really work because prizes are static. Aging pitchers are not. A very good 34 year old Darvish could easily turn into a 36 year old train wreck Darvish.
You know the Monty Hall Problem, right? On a giveaway show like Let's Make A Deal, there's 3 doors, behind which are two worthless goats and one Fabulous Prize - the contestant picks one at random, Monty (WHO KNOWS WHAT IS BEHIND WHICH DOOR) reveals one of the other doors has a goat, and then asks if the contestant wants to switch his choice to the other un-opened door. Should the contestant accept the swap? Does it matter? The answer is YES, which goes against many people's intuition. His chance of winning the prize goes up from 33% to 50%. A learning experience.
But, that's part of the showmanship. Monty knows that he's giving away more money by allowing the contestant to make that change. Absent showmanship, Monty is a fool to allow this swap.
It's a lesson in the economic value of revealed information. If Monty was in the dark about which door to open, then sometimes he'd accidentally reveal the Fabulous Prize. No, he always reveals one of the goats, because he's implicitly imparting new information to the contestant.
Different scenario with an opt-out clause, but same logic. Offering a second-guess after new information (say, 2 more years of performance data) is revealed is costly to the person offering it.
I'm not saying it's wrong to offer an opt-out. But recognize that the cost is hidden: the contract value is static but you've removed some of the upside. The upside being that the pitcher might defy the odds and lead his team to the World Series in Year 3, Year 4, or even 5 and 6. But you're still on the hook for all the risk of the bad things in Year 1 and 2 that perpetuate through the 6-year contract period.
On top of that, contracts generally pay the player fairly in the first half and then overpay in the second half. If the player wants to reset that contract risk with another team as he ages into his mid-30s and you already got a few seasons of solid value from the player, so be it. Take your modest victory and move on to the next guy. “Past performance does not guarantee future results” and all that.