By this logic, every signing could come with regret. They could sign anyone, and that player could get hurt, or just be bad. They could sign Ray for $15MM a year, and he could get hurt.....should we look at that signing and judge it when it is done, or after the fact? If after the fact, then we just don't agree on how one should judge people's actions. Which is fine.
It isn't irrational to look at the deal, with the knowledge we have at the time it was signed, and think it is a good deal.