Thanks for posting that. Here's what strikes me as the key take-away:
"However, the Seahawks pigeon-holed themselves when they sent a trade package that included a second-round pick to the Giants, giving Williams the leverage in contract negotiations and putting them in a position where they had to overpay to keep him or risk losing him for nothing in free agency after sacrificing legitimate draft capital to acquire him."
"Spotrac’s calculated market value
projected Williams to earn $16.7 million annually in his next contract, which he easily surpassed in his new deal with Seattle."
Would it have been better to let him walk? Truthfully, I don't know. I think it's right on the line. If he doesn't continue to perform at a super high level for the next three years, it will be seen in retrospect as another bad signing. The kind of splashy free-agent signing that the best teams don't do.